Master Bash Test Commands: Conditional Logic, Comparisons, and File Checks

Shell test command

Every reasonable programming language can test a condition and act on the result. Bash provides the test builtin, the [ ] and [[ ]] operators, arithmetic (( )) and the if … then … fi construct.

Related commands and symbols

If/then conditional statements.

Built‑in [ ] and enhanced [[ ]] brackets.

Arithmetic (( )) and let for numeric expressions.

Checking any command with if/then

#!/bin/bash
if cmp a.txt b.txt > /dev/null
then
    echo 'Files a and b are identical.'
else
    echo 'Files a and b are diff.'
fi

if/then syntax examples

if [ condition-true ]
then
    command1
    command2
    ...
else   # or elif …
    command3
    command4
    ...
fi

if [ condition1 ]
then
    command1
    command2
    command3
elif [ condition2 ]
then
    command4
    command5
else
    default-command
fi

Arithmetic tests with (( ))

#!/bin/bash
var1=7
var2=10
if (( var1 > var2 ))
then
    echo "var1 is greater than var2"
else
    echo "var1 is less than var2"
fi
exit 0

Numeric comparison operators

-eq

: equal, -ne: not equal, -gt: greater than, -ge: greater or equal, -lt: less than, -le: less or equal.

String comparison operators

str1 = str2

: equal, str1 != str2: not equal, -z str1: zero‑length, -n str1: non‑zero length, str1 > str2: lexicographically greater, str1 < str2: lexicographically less.

File test operators

-e file

: exists, -r file: readable, -w file: writable, -x file: executable, -s file: non‑empty, -d file: directory, -f file: regular file, -c file: character device, -b file: block device.

Examples of file type tests

#!/bin/bash
device1="/dev/sda1"
if [ -b "$device1" ]; then
    echo "$device1 is a block device."
fi

device2='/dev/tty0'
if [ -c "$device2" ]; then
    echo "$device2 is a character device."
fi