Q. I see [ command in /usr/bin directory. What is the /usr/bin/[ command used for?
Adblock detected 😱
My website is made possible by displaying online advertisements to my visitors. I get it! Ads are annoying but they help keep this website running. It is hard to keep the site running and producing new content when so many people block ads. Please consider donating money to the nixCraft via
PayPal/
Bitcoin, or become a
supporter using Patreon.
Advertisements
A.This is test command and it is used to check file types and compare values.
General syntax is as follows:
[ EXPRESSION ]
For example, find out if /etc/passwd exists or not:
[ -f /etc/passwd ] && echo "Yes" || echo "No"
Regularly you write it as follows:
if [ -f /etc/passwd ]
then
echo "Yes"
else
echo "No"
fi |
if [ -f /etc/passwd ]
then
echo "Yes"
else
echo "No"
fi
OR
if test -f /etc/passwd
then
echo "Yes"
else
echo "No"
fi |
if test -f /etc/passwd
then
echo "Yes"
else
echo "No"
fi
Read test or [ command man page for all other expressions.
man [
man test
ADVERTISEMENTS
Posted by: Vivek Gite
The author is the creator of nixCraft and a seasoned sysadmin, DevOps engineer, and a trainer for the Linux operating system/Unix shell scripting. Get the latest tutorials on SysAdmin, Linux/Unix and open source topics via RSS/XML feed or weekly email newsletter.
1 comment
Doesn’t work as written in all shells (e.g. BASH – not tested in others)
root@localhost:~/root# ls -l
total 0
-rw——-. 1 root root 0 Oct 25 14:19 test
root@localhost:~/root# [ -a test] echo “Y” || echo “N” // <– Fails
bash: [: missing `]'
N
root@localhost:~/root# [ -a test ]; echo "Y" || echo "N" // <– Requires ';' after ']'
Y
In Bash, the semi-colon ';' separates commands on the same line allowing multiple commands on a single line
–PB–