test Command in Linux with Examples

DESCRIPTION

Test is used in conditional execution. It is used for:
1. File attributes comparisons
2. Perform string comparisons.
3. Basic arithmetic comparisons.

test exits with the status determined by EXPRESSION. Placing the EXPRESSION between square brackets ([ and ]) is the same as testing the EXPRESSION with test. To see the exit status at the command prompt, echo the value “$?” A value of 0 means the expression evaluated as true, and a value of 1 means the expression evaluated as false.

SYNOPSIS

test EXPRESSION

EXPRESSIONS

Expressions take the following forms:

EXAMPLES

1. Simple example stating use of relational operator -gt

$ test 100 -gt 99 && echo "Yes, that's true." || echo "No, that's false."

This command will print the text “Yes, that’s true.” because 100 is greater than 99.

2. This example states the use of test command along-with echoing $? i.e. last command exit status.

[ "awesome" = "awesome" ]; echo $?

This command will print “0” because the expression is true; the two strings are identical.

3. Check if a FILE exists and is a regular file

$ test -f /etc/resolv.conf && echo "File /etc/resolv.conf found." || echo "File /etc/resolv.conf not found."
File /etc/resolv.conf found.

4. To test whether a file is nonexistent or empty, type the shell script:

 if test ! -s "$1"
 then
   echo $1 does not exist or is empty.
 fi

If the file specified by the first positional parameter to the shell procedure, $1, does not exist or is of size 0, the test command displays the message. If $1 exists and has a size greater than 0, the test command displays nothing.
Note: There must be a space between the -s function and the file name.
The quotation marks around $1 ensure that the test works properly even if the value of $1 is a null string. If the quotation marks are omitted and $1 is the empty string, the test command displays the error message

test: argument expected.

5. To do a complex comparison, type the shell script:

 if [ $# -lt 2 -o ! -e "$1" ]
 then
   exit
 fi

If the shell procedure is given fewer than two positional parameters or the file specified by $1 does not exist, then the shell procedure exits. The special shell variable $# represents the number of positional parameters entered on the command line that starts this shell procedure.