How can I check the first character in a string in Bash or Unix shell?
StringBashUnixCharacterExitstatusString Problem Overview
I'm writing a script in Unix where I have to check whether the first character in a string is "/" and if it is, branch.
For example, I have a string:
/some/directory/file
I want this to return 1, and:
server@10.200.200.20:/some/directory/file
to return 0.
String Solutions
Solution 1 - String
There are many ways to do this. You could use wildcards in double brackets:
str="/some/directory/file"
if [[ $str == /* ]]; then echo 1; else echo 0; fi
You can use substring expansion:
if [[ ${str:0:1} == "/" ]] ; then echo 1; else echo 0; fi
Or a regex:
if [[ $str =~ ^/ ]]; then echo 1; else echo 0; fi
Solution 2 - String
Consider the case statement as well which is compatible with most sh-based shells:
case $str in
/*)
echo 1
;;
*)
echo 0
;;
esac
Solution 3 - String
$ foo="/some/directory/file"
$ [ ${foo:0:1} == "/" ] && echo 1 || echo 0
1
$ foo="[email protected]:/some/directory/file"
$ [ ${foo:0:1} == "/" ] && echo 1 || echo 0
0
Solution 4 - String
cut -c1
This is POSIX, and unlike case, it actually extracts the first character if you need it for later:
myvar=abc
first_char="$(printf '%s' "$myvar" | cut -c1)"
if [ "$first_char" = a ]; then
echo 'starts with a'
else
echo 'does not start with a'
fi
awk substr is another POSIX command, but less efficient alternative:
printf '%s' "$myvar" | awk '{print substr ($0, 0, 1)}'
printf '%s' is to avoid problems with escape characters: https://stackoverflow.com/questions/40423203/bash-printf-literal-verbatim-string/40423558#40423558, e.g.,
myvar='\n'
printf '%s' "$myvar" | cut -c1
outputs \ as expected.
${::} does not seem to be POSIX.
Solution 5 - String
Code:
place="Place"
fchar=${place:0:1}
echo $fchar
Output:
P