5 “test” Command Usage Examples in Linux

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This tutorial explains Linux “test” command, options and its usage with examples.

test – Checks file types and compares values.

DESCRIPTION

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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

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EXPRESSIONS

Expressions take the following forms:

( EXPRESSION ) EXPRESSION is true
! EXPRESSION EXPRESSION is false
EXPRESSION1 -a EXPRESSION2 both EXPRESSION1 and EXPRESSION2 are true
EXPRESSION1 -o EXPRESSION2 either EXPRESSION1 or EXPRESSION2 is true
-n STRING the length of STRING is nonzero
STRING equivalent to -n STRING
-z STRING the length of STRING is zero
STRING1 = STRING2 the strings are equal
STRING1 != STRING2 the strings are not equal
INTEGER1 -eq INTEGER2 INTEGER1 is equal to INTEGER2
INTEGER1 -ge INTEGER2 INTEGER1 is greater than or equal to INTEGER2
INTEGER1 -gt INTEGER2 INTEGER1 is greater than INTEGER2
INTEGER1 -le INTEGER2 INTEGER1 is less than or equal to INTEGER2
INTEGER1 -lt INTEGER2 INTEGER1 is less than INTEGER2
INTEGER1 -ne INTEGER2 INTEGER1 is not equal to INTEGER2
FILE1 -ef FILE2 FILE1 and FILE2 have the same device and inode numbers
FILE1 -nt FILE2 FILE1 is newer (modification date) than FILE2
FILE1 -ot FILE2 FILE1 is older than FILE2
-b FILE FILE exists and is block special
-c FILE FILE exists and is character special
-d FILE FILE exists and is a directory
-e FILE FILE exists
-f FILE FILE exists and is a regular file
-g FILE FILE exists and is set-group-ID
-G FILE FILE exists and is owned by the effective group ID
-h FILE FILE exists and is a symbolic link (same as -L)
-k FILE FILE exists and has its sticky bit set
-L FILE FILE exists and is a symbolic link (same as -h)
-O FILE FILE exists and is owned by the effective user ID
-p FILE FILE exists and is a named pipe
-r FILE FILE exists and read permission is granted
-s FILE FILE exists and has a size greater than zero
-S FILE FILE exists and is a socket
-t FD file descriptor FD is opened on a terminal
-u FILE FILE exists and its set-user-ID bit is set
-w FILE FILE exists and write permission is granted
-x FILE FILE exists and execute (or search) permission is granted

EXAMPLES

1. Simple example stating use of relational operator -gt

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$ 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.

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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

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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.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn | Youtube | Instagram | Facebook | Twitter