12/5/2022 Basic shell tests

Memorize how to perform various tests in shell scripting :

The following conditionnal pattern is POSIX compliant :

if [ condition ]; then
  do something
else 
  do other thing
fi

or with then on next line :

if [ condition ]
then
  do something
else 
  do other thing
fi

Note that [ is the same as test (see in Sources, below).

Test if a command does not exists : -x means executable.

if ! [ -x  $(command -v git) ]; then
  echo "Warning: git command is not found"
fi

Test if a file (remember, a unix file can be anything) exists : -e means existing.

if ! [ -e  filename ]; then
  echo "Warning: filename is not found"
fi

To be more precise, use -d or -f (directory, regular file)

Note: In a fish shell script, syntax would be much simpler :

if test -d $HOME/DEV/rust
  set -l FOO bar
    set -gx FIZ buzz
else
    set -gx BAR foo
end

Sources :

man test