What is your single most favorite command-line trick using Bash?

We all know how to use <ctrl>-R to reverse search through history, but did you know you can use <ctrl>-S to forward search if you set stty stop ""? Also, have you ever tried running bind -p to see all of your keyboard shortcuts listed? There are over 455 on Mac OS X by default.

What is your single most favorite obscure trick, keyboard shortcut or shopt configuration using bash?

Renaming/moving files with suffixes quickly:
cp /home/foo/realllylongname.cpp{,-old}

This expands to:
cp /home/foo/realllylongname.cpp /home/foo/realllylongname.cpp-old

cd -

It's the command-line equivalent of the back button (takes you to the previous directory you were in).

Another favorite:

!!

Repeats your last command. Most useful in the form:

sudo !!

My favorite is '^string^string2' which takes the last command, replaces string with string2 and executes it

$ ehco foo bar baz
bash: ehco: command not found
$ ^ehco^echo
foo bar baz

Bash command line history guide

rename

Example:

$ ls
this_has_text_to_find_1.txt
this_has_text_to_find_2.txt
this_has_text_to_find_3.txt
this_has_text_to_find_4.txt




$ rename 's/text_to_find/been_renamed/' *.txt
$ ls
this_has_been_renamed_1.txt
this_has_been_renamed_2.txt
this_has_been_renamed_3.txt
this_has_been_renamed_4.txt

So useful

I'm a fan of the !$, !^ and !* expandos, returning, from the most recent submitted command line: the last item, first non-command item, and all non-command items. To wit (Note that the shell prints out the command first):

$ echo foo bar baz
foo bar baz
$ echo bang-dollar: !$ bang-hat: !^ bang-star: !*
echo bang-dollar: baz bang-hat: foo bang-star: foo bar baz
bang-dollar: baz bang-hat: foo bang-star: foo bar baz

This comes in handy when you, say ls filea fileb, and want to edit one of them: vi !$ or both of them: vimdiff !*. It can also be generalized to "the nth argument" like so:

$ echo foo bar baz
$ echo !:2
echo bar
bar

Finally, with pathnames, you can get at parts of the path by appending :h and :t to any of the above expandos:

$ ls /usr/bin/id
/usr/bin/id
$ echo Head: !$:h  Tail: !$:t
echo Head: /usr/bin Tail: id
Head: /usr/bin Tail: id

When running commands, sometimes I'll want to run a command with the previous ones arguments. To do that, you can use this shortcut:

$ mkdir /tmp/new
$ cd !!:*

Occasionally, in lieu of using find, I'll break-out a one-line loop if I need to run a bunch of commands on a list of files.

for file in *.wav; do lame "$file" "$(basename "$file" .wav).mp3" ; done;

Configuring the command-line history options in my .bash_login (or .bashrc) is really useful. The following is a cadre of settings that I use on my Macbook Pro.

Setting the following makes bash erase duplicate commands in your history:

export HISTCONTROL="erasedups:ignoreboth"

I also jack my history size up pretty high too. Why not? It doesn't seem to slow anything down on today's microprocessors.

export HISTFILESIZE=500000
export HISTSIZE=100000

Another thing that I do is ignore some commands from my history. No need to remember the exit command.

export HISTIGNORE="&:[ ]*:exit"

You definitely want to set histappend. Otherwise, bash overwrites your history when you exit.

shopt -s histappend

Another option that I use is cmdhist. This lets you save multi-line commands to the history as one command.

shopt -s cmdhist

Finally, on Mac OS X (if you're not using vi mode), you'll want to reset <CTRL>-S from being scroll stop. This prevents bash from being able to interpret it as forward search.

stty stop ""

How to list only subdirectories in the current one ?

ls -d */

It's a simple trick, but you wouldn't know how much time I needed to find that one !

ESC.

Inserts the last arguments from your last bash command. It comes in handy more than you think.

cp file /to/some/long/path

cd ESC.

Sure, you can "diff file1.txt file2.txt", but Bash supports process substitution, which allows you to diff the output of commands.

For example, let's say I want to make sure my script gives me the output I expect. I can just wrap my script in <( ) and feed it to diff to get a quick and dirty unit test:

$ cat myscript.sh
#!/bin/sh
echo -e "one\nthree"
$
$ ./myscript.sh 
one
three
$
$ cat expected_output.txt
one
two
three
$
$ diff <(./myscript.sh) expected_output.txt
1a2
> two
$

As another example, let's say I want to check if two servers have the same list of RPMs installed. Rather than sshing to each server, writing each list of RPMs to separate files, and doing a diff on those files, I can just do the diff from my workstation:

$ diff <(ssh server1 'rpm -qa | sort') <(ssh server2 'rpm -qa | sort')
241c240
< kernel-2.6.18-92.1.6.el5
---
> kernel-2.6.18-92.el5
317d315
< libsmi-0.4.5-2.el5
727,728d724
< wireshark-0.99.7-1.el5
< wireshark-gnome-0.99.7-1.el5
$

There are more examples in the Advanced Bash-Scripting Guide at <http://tldp.org/LDP/abs/html/process-sub.html>;.

My favorite command is "ls -thor"

It summons the power of the gods to list the most recently modified files in a conveniently readable format.

More of a novelty, but it's clever...

Top 10 commands used:

$ history | awk '{print $2}' | awk 'BEGIN {FS="|"}{print $1}' | sort | uniq -c | sort -nr | head

Sample output:

 242 git
  83 rake
  43 cd
  33 ss
  24 ls
  15 rsg
  11 cap
  10 dig
   9 ping
   3 vi

^R reverse search. Hit ^R, type a fragment of a previous command you want to match, and hit ^R until you find the one you want. Then I don't have to remember recently used commands that are still in my history. Not exclusively bash, but also: ^E for end of line, ^A for beginning of line, ^U and ^K to delete before and after the cursor, respectively.

I often have aliases for vi, ls, etc. but sometimes you want to escape the alias. Just add a back slash to the command in front:

Eg:

$ alias vi=vim
$ # To escape the alias for vi:
$ \vi # This doesn't open VIM

Cool, isn't it?

Here's a couple of configuration tweaks:

~/.inputrc:

"\C-[[A": history-search-backward
"\C-[[B": history-search-forward

This works the same as ^R but using the arrow keys instead. This means I can type (e.g.) cd /media/ then hit up-arrow to go to the last thing I cd'd to inside the /media/ folder.

(I use Gnome Terminal, you may need to change the escape codes for other terminal emulators.)

Bash completion is also incredibly useful, but it's a far more subtle addition. In ~/.bashrc:

if [ -f /etc/bash_completion ]; then
    . /etc/bash_completion
fi

This will enable per-program tab-completion (e.g. attempting tab completion when the command line starts with evince will only show files that evince can open, and it will also tab-complete command line options).

Works nicely with this also in ~/.inputrc:

set completion-ignore-case on
set show-all-if-ambiguous on
set show-all-if-unmodified on

I use the following a lot:

The :p modifier to print a history result. E.g.

!!:p

Will print the last command so you can check that it's correct before running it again. Just enter !! to execute it.

In a similar vein:

!?foo?:p

Will search your history for the most recent command that contained the string 'foo' and print it.

If you don't need to print,

!?foo

does the search and executes it straight away.

I have got a secret weapon : shell-fu.

There are thousand of smart tips, cool tricks and efficient recipes that most of the time fit on a single line.

One that I love (but I cheat a bit since I use the fact that Python is installed on most Unix system now) :

alias webshare='python -m SimpleHTTPServer'

Now everytime you type "webshare", the current directory will be available through the port 8000. Really nice when you want to share files with friends on a local network without usb key or remote dir. Streaming video and music will work too.

And of course the classic fork bomb that is completely useless but still a lot of fun :

$ :(){ :|:& };:

Don't try that in a production server...

You can use the watch command in conjunction with another command to look for changes. An example of this was when I was testing my router, and I wanted to get up-to-date numbers on stuff like signal-to-noise ratio, etc.

watch --interval=10 lynx -dump http://dslrouter/stats.html

I like to construct commands with echo and pipe them to the shell:

$ find dir -name \*~ | xargs echo rm
...
$ find dir -name \*~ | xargs echo rm | ksh -s

Why? Because it allows me to look at what's going to be done before I do it. That way if I have a horrible error (like removing my home directory), I can catch it before it happens. Obviously, this is most important for destructive or irrevocable actions.

type -a PROG

in order to find all the places where PROG is available, usually somewhere in ~/bin rather than the one in /usr/bin/PROG that might have been expected.

When downloading a large file I quite often do:

while ls -la <filename>; do sleep 5; done

And then just ctrl+c when I'm done (or if ls returns non-zero). It's similar to the watch program but it uses the shell instead, so it works on platforms without watch.

Another useful tool is netcat, or nc. If you do:

nc -l -p 9100 > printjob.prn

Then you can set up a printer on another computer but instead use the IP address of the computer running netcat. When the print job is sent, it is received by the computer running netcat and dumped into printjob.prn.

pushd and popd almost always come in handy

One preferred way of navigating when I'm using multiple directories in widely separate places in a tree hierarchy is to use acf_func.sh (listed below). Once defined, you can do

cd --

to see a list of recent directories, with a numerical menu

cd -2

to go to the second-most recent directory.

Very easy to use, very handy.

Here's the code:

# do ". acd_func.sh"
# acd_func 1.0.5, 10-nov-2004
# petar marinov, http:/geocities.com/h2428, this is public domain

cd_func ()
{
  local x2 the_new_dir adir index
  local -i cnt

  if [[ $1 ==  "--" ]]; then
    dirs -v
    return 0
  fi

  the_new_dir=$1
  [[ -z $1 ]] && the_new_dir=$HOME

  if [[ ${the_new_dir:0:1} == '-' ]]; then
    #
    # Extract dir N from dirs
    index=${the_new_dir:1}
    [[ -z $index ]] && index=1
    adir=$(dirs +$index)
    [[ -z $adir ]] && return 1
    the_new_dir=$adir
  fi

  #
  # '~' has to be substituted by ${HOME}
  [[ ${the_new_dir:0:1} == '~' ]] && the_new_dir="${HOME}${the_new_dir:1}"

  #
  # Now change to the new dir and add to the top of the stack
  pushd "${the_new_dir}" > /dev/null
  [[ $? -ne 0 ]] && return 1
  the_new_dir=$(pwd)

  #
  # Trim down everything beyond 11th entry
  popd -n +11 2>/dev/null 1>/dev/null

  #
  # Remove any other occurence of this dir, skipping the top of the stack
  for ((cnt=1; cnt <= 10; cnt++)); do
    x2=$(dirs +${cnt} 2>/dev/null)
    [[ $? -ne 0 ]] && return 0
    [[ ${x2:0:1} == '~' ]] && x2="${HOME}${x2:1}"
    if [[ "${x2}" == "${the_new_dir}" ]]; then
      popd -n +$cnt 2>/dev/null 1>/dev/null
      cnt=cnt-1
    fi
  done

  return 0
}

alias cd=cd_func

if [[ $BASH_VERSION > "2.05a" ]]; then
  # ctrl+w shows the menu
  bind -x "\"\C-w\":cd_func -- ;"
fi

Expand complicated lines before hitting the dreaded enter

• Alt+Ctrl+e — shell-expand-line (may need to use Esc, Ctrl+e on your keyboard)
• Ctrl+_ — undo
• Ctrl+x, * — glob-expand-word

$ echo !$ !-2^ * Alt+Ctrl+e
$ echo aword someotherword * Ctrl+_
$ echo !$ !-2^ * Ctrl+x, *
$ echo !$ !-2^ LOG Makefile bar.c foo.h

&c.

I've always been partial to:

ctrl-E # move cursor to end of line
ctrl-A # move cursor to beginning of line

I also use shopt -s cdable_vars, then you can create bash variables to common directories. So, for my company's source tree, I create a bunch of variables like:

export Dcentmain="/var/localdata/p4ws/centaur/main/apps/core"

then I can change to that directory by cd Dcentmain.

pbcopy

This copies to the Mac system clipboard. You can pipe commands to it...try:

pwd | pbcopy

$ touch {1,2}.txt
$ ls [12].txt
1.txt  2.txt
$ rm !:1
rm [12].txt
$ history | tail -10
...
10007  touch {1,2}.txt
...
$ !10007
touch {1,2}.txt
$ for f in *.txt; do mv $f ${f/txt/doc}; done

Using 'set -o vi' from the command line, or better, in .bashrc, puts you in vi editing mode on the command line. You start in 'insert' mode so you can type and backspace as normal, but if you make a 'large' mistake you can hit the esc key and then use 'b' and 'f' to move around as you do in vi. cw to change a word. Particularly useful after you've brought up a history command that you want to change.

String multiple commands together using the && command:

./run.sh && tail -f log.txt

or

kill -9 1111 && ./start.sh

Similar to many above, my current favorite is the keystroke [alt]. (Alt and "." keys together) this is the same as $! (Inserts the last argument from the previous command) except that it's immediate and for me easier to type. (Just can't be used in scripts)

eg:

mkdir -p /tmp/test/blah/oops/something
cd [alt].

Duplicate file finder

This will run checksums recursively from the current directory, and give back the filenames of all identical checksum results:

find ./ -type f -print0 | xargs -0 -n1 md5sum | sort -k 1,32 | uniq -w 32 -d --all-repeated=separate | sed -e 's/^[0-9a-f]*\ *//;'

You can, of course, change the path around.
Maybe put it into a function or alias, and pass in the target path as a parameter.

!<first few characters of the command> will execute the last command which matches.

Example:

!b will run "build whatever -O -p -t -i -on" !. will run ./a.out

It works best with long and repetitive commands, like compile, build, execute, etc. It saved me sooo much time when coding and testing.

I have plenty of directories which I want to access quickly, CDPATH variable is solution that speed up my work-flow enormously:

export CDPATH=.:/home/gadolin/sth:/home/gadolin/dir1/importantDir

now with cd I can jump to any of sub directories of /home/gadolin/sth or /home/gadolin/dir1/importantDir without providing the full path. And also <tab> works here just like I would be there! So if there are directories /home/gadolin/sth/1 /home/gadolin/sth/2, I type cd 1 wherever, and I am there.

Ctrl + L will usually clear the screen. Works from the Bash prompt (obviously) and in GDB, and a lot of other prompts.

You should be able to paste the following into a bash terminal window.

Display ANSI colour palette:

e="\033["
for f in 0 7 `seq 6`; do
  no="" bo=""
  for b in n 7 0 `seq 6`; do
    co="3$f"; p="  "
    [ $b = n ] || { co="$co;4$b";p=""; }
    no="${no}${e}${co}m   ${p}${co} ${e}0m"
    bo="${bo}${e}1;${co}m ${p}1;${co} ${e}0m"
  done
  echo -e "$no\n$bo"
done

256 colour demo:

yes "$(seq 232 255;seq 254 -1 233)" |
while read i; do printf "\x1b[48;5;${i}m\n"; sleep .01; done

Delete everything except important-file:

# shopt -s extglob
# rm -rf !(important-file)

The same in zsh:

# rm -rf *~important-file

Bevore I knew that I had to move the important fiels to an other dictionary, delete everything and move the important back again.

Using history substiution characters !# to access the current command line, in combination with ^, $, etc.

E.g. move a file out of the way with an "old-" prefix:

mv file-with-long-name-typed-with-tab-completion.txt old-!#^

http://www.commandlinefu.com is also a great site.

I learned quite useful things there like:

sudo !!

or

mount | column -t

Well, this may be a bit off topic, but if you are an Emacs user, I would say "emacs" is the most powerful trick... before you downvote this, try out "M-x shell" within an emacs instance... you get a shell inside emacs, and have all the power of emacs along with the power of a shell (there are some limitations, such as opening another emacs within it, but in most cases it is a lot more powerful than a vanilla bash prompt).

I like a splash of colour in my prompts:

export PS1="\[\033[07;31m\] \h \[\033[47;30m\] \W \[\033[00;31m\] \$ \[\e[m\]"

I'm afraid I don't have a screenshot for what that looks like, but it's supposed to be something like (all on one line):

[RED BACK WHITE TEXT] Computer name 
[BLACK BACK WHITE TEXT] Working Directory 
[WHITE BACK RED TEXT] $

Customise as per what you like to see :)

As an extension to CTRL-r to search backwards, you can auto-complete your current input with your history if you bind 'history-search-backward'. I typically bind it to the same key that it is in tcsh: ESC-p. You can do this by putting the following line in your .inputrc file:

"\M-p": history-search-backward

E.g. if you have previously executed 'make some_really_painfully_long_target' you can type:

> make <ESC p>

and it will give you

> make some_really_painfully_long_target

A simple thing to do when you realize you just typed the wrong line is hit Ctrl+C; if you want to keep the line, but need to execute something else first, begin a new line with a back slash - , then Ctrl+C. The line will remain in your history.

Insert preceding lines final parameter

ALT-. the most useful key combination ever, try it and see, for some reason no one knows about this one.

Press it again and again to select older last parameters.

Great when you want to do something else to something you used just a moment ago.

Curly-Brace Expansion:

Really comes in handy when running a ./configure with a lot of options:

./configure --{prefix=/usr,mandir=/usr/man,{,sh}libdir=/usr/lib64,\
enable-{gpl,pthreads,bzlib,lib{faad{,bin},mp3lame,schroedinger,speex,theora,vorbis,xvid,x264},\
pic,shared,postproc,avfilter{-lavf,}},disable-static}

This is quite literally my configure settings for ffmpeg. Without the braces it's 409 characters.

Or, even better:

echo "I can count to a thousand!" ...{0,1,2,3,4,5,6,7,8,9}{0,1,2,3,4,5,6,7,8,9}{0,1,2,3,4,5,6,7,8,9}...

I have various typographical error corrections in aliases

alias mkae=make

alias mroe=less

The easiest keystrokes for me for "last argument of the last command" is !$

echo what the heck?

what the heck?

echo !$

heck?

$_ (dollar underscore): the last word from the previous command. Similar to !$ except it doesn't put its substitution in your history like !$ does.

Eliminate duplicate lines from a file

#sort -u filename > filename.new

List all lines that do not match a condition

#grep -v ajsk filename

These are not necessarily Bash specific (but hey neither is ls -thor :) )

Some other useful cmds:

prtdiag, psrinfo, prtconf - more info here and here (posts on my blog).

Not really obscure, but one of the features I absolutely love is tab completion.
Really useful when you are navigating trough an entire subtree structure, or when you are using some obscure, or long command!

CTRL+D quits the shell.

Using alias can be time-saving

alias myDir = "cd /this/is/a/long/directory; pwd"

I'm a big fan of Bash job control, mainly the use of Control-Z and fg, especially if I'm doing development in a terminal. If I've got emacs open and need to compile, deploy, etc. I just Control-Z to suspend emacs, do what I need, and fg to bring it back. This keeps all of the emacs buffers intact and makes things much easier than re-launching whatever I'm doing.

alias ..='cd ..'

So when navigating back up a directory just use ..<Enter>

SSH tunnel:

ssh -fNR 1234:localhost:22 root@123.123.123.123

Not my favorite, by very helpful if you're trying any of the other answers using copy and paste:

function $
{
    "$@"
}

Now you can paste examples that include a $ prompt at the start of each line.

bash can redirect to and from TCP/IP sockets. /dev/tcp/ and /dev/udp.

Some people think it's a security issue, but that's what OS level security like Solaris X's jail is for.

As Will Robertson notes, change prompt to do stuff... print the command # for !nn Set the Xterm terminal name. If it's an old Xterm that doesn't sniff traffic to set it's title.

And this one is key for me actually:

set -o vi

/Allan

I've always liked this one. Add this to your /etc/inputrc or ~/.inputrc

"\e[A":history-search-backward "\e[B":history-search-forward

When you type ls <up-arrow> it will be replaced with the last command starting with "ls " or whatever else you put in.

This prevents less (less is more) from clearing the screen at the end of a file:

export LESS="-X"

When navigating between two separate directories and copying files back and forth, I do this:

cd /some/where/long
src=`pwd`
cd /other/where/long
dest=`pwd`
 
cp $src/foo $dest

command completion will work by expanding the variable, so you can use tab completion to specify a file you're working with.

<anything> | sort | uniq -c | sort -n

will give you a count of all the different occurrences of <anything>.

Often, awk, sed, or cut help with the parsing of data in <anything>.

du -a | sort -n | tail -99

to find the big files (or directories of files) to clean up to free up disk space.

A few years ago, I discovered the p* commands or get information about processes: ptree, pgrep, pkill, and pfiles. Of course, the mother of them all is ps, but you need to pipe the output into less, grep and/or awk to make sense of the output under heavy load. top (and variants) help too.

Want to get the last few lines of a log file?

tail /var/log/syslog

Want to keep an eye on a log file for when it changes?

tail -f /var/log/syslog

Want to quickly read over a file from the start?

more /var/log/syslog

Want to quickly find if a file contains some text?

grep "find this text" /var/log/syslog

The FIGNORE environment variable is nice when you want TAB completion to ignore files or folders with certain suffixes, e.g.:

export FIGNORE="CVS:.svn:~"

Use the IFS environment variable when you want to define an item separator other than space, e.g.:

export IFS="
"

This will make you able to loop through files and folders with spaces in them without performing any magic, like this:

$ touch "with spaces" withoutspaces
$ for i in `ls *`; do echo $i; done
with
spaces
withoutspaces
$ IFS="
"
$ for i in `ls *`; do echo $i; done
with spaces
withoutspaces

Good for making an exact recursive copy/backup of a directory including symlinks (rather than following them or ignoring them like cp):

$ mkdir new_dir
$ cd old_dir
$ tar cf - . | ( cd ../old_dir; tar xf - )

Top 10 commands again (like ctcherry's post, only shorter):

history | awk '{ print $2 }' | sort | uniq -c |sort -rn | head

I'm new to programming on a mac, and I miss being able to launch gui programs from bash...so I have to create functions like this:

function macvim
{
/Applications/MacVim.app/Contents/MacOS/Vim "$@" -gp &
}

while IFS= read -r line; do
echo "$line"
done < somefile.txt

This is a good way to process a file line by line. Clearing IFS is needed to get whitespace characters at the front or end of the line. The "-r" is needed to get all raw characters, including backslashes.

Some Bash nuggets also here:

http://codesnippets.joyent.com/tag/bash

One of my favorites tricks with bash is the "tar pipe". When you have a monstrous quantity of files to copy from one directory to another, doing "cp * /an/other/dir" doesn't work if the number of files is too high and explode the bash globber, so, the tar pipe :

(cd /path/to/source/dir/ ; tar cf - * ) | (cd /path/to/destination/ ; tar xf - )

...and if you have netcat, you can even do the "netcat tar pipe" through the network !!

I have a really stupid, but extremely helpful one when navigating deep tree structures. Put this in .bashrc (or similar):

alias cd6="cd ../../../../../.."
alias cd5="cd ../../../../.."
alias cd4="cd ../../../.."
alias cd3="cd ../../.."
alias cd2="cd ../.."

On Mac OS X,

ESC .

will cycle through recent arguments in place. That's: press and release ESC, then press and release . (period key). On Ubuntu, I think it's ALT+..

You can do that more than once, to go back through all your recent arguments. It's kind of like CTRL + R, but for arguments only. It's also much safer than !! or $!, since you see what you're going to get before you actually run the command.

sudo !!

Runs the last command with administrator privileges.

Shell-fu is a place for storing, moderating and propagating command line tips and tricks. A bit like StackOverflow, but solely for shell. You'll find plenty of answers to this question there.

Since I always need the for i in $(ls) statement I made a shortcut:

fea(){
   if test -z ${2:0:1}; then action=echo; else action=$2; fi
   for i in $(ls $1);
      do $action $i ;
   done;
}

Another one is:

echo ${!B*}

It will print a list of all defined variables that start with 'B'.

ctrl-u delete all written stuff

Quick Text

I use these sequences of text all too often, so I put shortcuts to them in by .inputrc:

# redirection short cuts
"\ew":            "2>&1"
"\eq":            "&>/dev/null &"
"\e\C-q":         "2>/dev/null"
"\eg":            "&>~/.garbage.out &"
"\e\C-g":         "2>~/.garbage.out"

$if term=xterm
"\M-w":           "2>&1"
"\M-q":           "&>/dev/null &"
"\M-\C-q":        "2>/dev/null"
"\M-g":           "&>~/.garbage.out &"
"\M-\C-g":        "2>~/.garbage.out"
$endif

Programmable Completion:

Nothing fancy. I always disable it when I'm using Knoppix because it gets in the way too often. Just some basic ones:

shopt -s progcomp

complete -A stopped -P '%'          bg
complete -A job     -P '%'          fg jobs disown wait
complete -A variable                readonly export
complete -A variable -A function    unset
complete -A setopt                  set
complete -A shopt                   shopt
complete -A helptopic               help
complete -A alias                   alias unalias
complete -A binding                 bind
complete -A command                 type which \
                                    killall pidof
complete -A builtin                 builtin
complete -A disabled                enable

Not really interactive shell tricks, but valid nonetheless as tricks for writing good scripts.

getopts, shift, $OPTIND, $OPTARG:

I love making customizable scripts:

while getopts 'vo:' flag; do
    case "$flag" in
        'v')
        VERBOSE=1
        ;;
        'o')
        OUT="$OPTARG"
        ;;
    esac
done
shift "$((OPTIND-1))"

---

xargs(1):

I have a triple-core processor and like to run scripts that perform compression, or some other CPU-intensive serial operation on a set of files. I like to speed it up using xargs as a job queue.

if [ "$#" -gt 1 ]; then
    # schedule using xargs
    (for file; do
        echo -n "$file"
        echo -ne '\0'
    done) |xargs -0 -n 1 -P "$NUM_JOBS" -- "$0"
else
    # do the actual processing
fi

This acts a lot like make -j [NUM_JOBS].

Signal trapping:

You can trap signals sent to the shell process and have them silently run commands in their respective environment as if typed on the command line:

# TERM or QUIT probably means the system is shutting down; make sure history is
# saved to $HISTFILE (does not do this by default)
trap 'logout'                      TERM QUIT

# save history when signalled by cron(1) script with USR1
trap 'history -a && history -n'    USR1

For the sheer humor factor, create an empty file "myself" and then: $ touch myself

extended globbing:

rm !(foo|bar)

expands like * without foo or bar:

$ ls
foo
bar
foobar
FOO
$ echo !(foo|bar)
foobar FOO

pbcopy and pbpaste aliases for GNU/Linux

alias pbcopy='xclip -selection clipboard'
alias pbpaste='xclip -selection clipboard -o'

Someone else recommended "M-x shell RET" in Emacs. I think "M-x eshell RET" is even better.

Some useful mencoder commands I found out about when looking for some audio and video editing tools:

from .xxx to .avi

mencoder movie.wmv -o movie.avi -ovc lavc -oac lavc 

Dump sound from a video:

mplayer -ao pcm -vo null -vc dummy -dumpaudio -dumpfile fileout.mp3 filein.avi 

I prefer reading man pages in vi, so I have the following in my .profile or .bashrc file

man () {
    sought=$*
    /usr/bin/man $sought | col -b | vim -R -c "set nonumber" -c "set syntax=man"  -
}

alias mycommand = 'verylongcommand -with -a -lot -of -parameters'
alias grep='grep --color'

find more than one word with grep :

netstat -c |grep 'msn\|skype\|icq'

You changed to a new directory and want to move a file from the new directory to the old one. In one move: mv file $OLDPWD

If I am searching for something in a directory, but I am not sure of the file, then I just grep the files in the directory by:

find . -exec grep whatIWantToFind {} \;

alias -- ddt='ls -trFld'
dt () { ddt --color "$@" | tail -n 30; }

Gives you the most recent files in the current directory. I use it all the time...

To be able to quickly edit a shell script you know is in your $PATH (do not try with ls...):

function viscr { vi $(which $*); }

Apropos history -- using cryptic carets, etc. is not entirely intuitive. To print all history items containing a given string:

function histgrep { fc -l -$((HISTSIZE-1)) | egrep "$@" ;}

Custom Tab Completion (compgen and complete bash builtins)

Tab Completion is nice, but being able to apply it to more than just filenames is great. I have used it to create custom functions to expand arguments to commands I use all the time. For example, lets say you often need to add the FQDN as an argument to a command (e.g. ping blah.really.long.domain.name.foo.com). You can use compgen and complete to create a bash function that reads your /etc/hosts file for results so all you have to type then is:

ping blah.<tab>

and it will display all your current match options.

So basically anything that can return a word list can be used as a function.

When running a command with lots of output (like a big "make") I want to not only save the output, but also see it:

make install 2>&1 | tee E.make

As a quick calculator, say to compute a percentage:

$ date
Thu Sep 18 12:55:33 EDT 2008
$ answers=60
$ curl "http://stackoverflow.com/questions/68372/what-are-some-of-your-favorite-command-line-tricks-using-bash"  > tmp.html
$ words=`awk '/class="post-text"/ {s = s $0} \
> /<\/div>/ { gsub("<[^>]*>", "", s); print s; s = ""} \
> length(s) > 0 {s = s $0}' tmp.html \
> |  awk '{n = n + NF} END {print n}'`
$ answers=`awk '/([0-9]+) Answers/ {sub("<h2>", "", $1); print $1}' tmp.html`

and finally:

$ echo $words words, $answers answers, $((words / $answers)) words per answer
4126 words, 60 answers, 68 words per answer
$

Not that division is truncated, not rounded. But often that's good enough for a quick calculation.

I always set my default prompt to "username@hostname:/current/path/name/in/full> "

PS1='\u@\h:\w> '
export PS1

Saves lots of confusion when you're dealing with lots of different machines.

find -iregex '.*\.py$\|.*\.xml$' | xargs egrep -niH 'a.search.pattern'  | vi -R -

Searches a pattern in all Python files and all XML files and pipes the result in a readonly Vim session.

Two of my favorites are:

1. Make tab-completion case insensitive (e.g. "cd /home/User " converts your command line to: "cd /home/user" if the latter exists and the former doesn't. You can turn it on with "set completion-ignore-case on" at the prompt, or add it permanently by adding "set completion-ignore-case on" to your .inputrc file.

2. The built-in 'type' command is like "which" but aware of aliases also. For example

   $ type cdhome cdhome is aliased to 'cd ~' $ type bash bash is /bin/bash

I like to set a prompt which shows the current directory in the window title of an xterm. It also shows the time and current directory. In addition, if bash wants to report that a background job has finished, it is reported in a different colour using ANSI escape sequences. I use a black-on-light console so my colours may not be right for you if you favour light-on-black.

PROMPT_COMMAND='echo -e "\033]0;${USER}@${HOSTNAME%%.*}:${PWD/#$HOME/~}\007\033[1;31m${PWD/#$HOME/~}\033[1;34m"'
PS1='\[\e[1;31m\]\t \$ \[\e[0m\]'

Make sure you understand how to use \[ and \] correctly in your PS1 string so that bash knows how long your prompt-string actually renders on screen. This is so it can redraw your command-line correctly when you move beyond a single line command.