Conditionally perform a command.

      if test-commands; then
      [elif more-test-commands; then
      [else alternate-consequents;]

Or in a single line:
     if test-commands; then consequent-commands; fi

The test-commands list is executed, and if its return status is zero (success), the consequent-commands list is executed.

Although if is most often used with test to return a True/False decision, it can be used with any command that returns an exit code of 0 for success.

If test-commands returns a non-zero status, each elif list is executed in turn, and if its exit status is zero, the corresponding more-consequents is executed and the command completes.

If 'else alternate-consequents' is present, and the final command in the final if or elif clause has a non-zero exit status, the alternate-consequents is executed.

For simple comparisons, a concise alternative is to use test along with the conditional operator && instead of IF.

The return status is the exit status of the last command executed, or zero if no condition tested true.

This is a BASH shell builtin, to display your local syntax from the bash prompt type: help if


Compare a variable with a string:

[[ "$var" = "snark" ]] && echo "found snark"

or the equivalent using if:

if [[ "$var" = "snark" ]]
  then echo "found snark"

Test if the file music.txt exists:

If [[ -e music.txt ]]; then
  echo "we found the file"

A single-line if command:

if [ $dayofmonth -lt 8 ]; then firstweek=1; fi

“Then you admit confirming not denying you ever said that?"
"NO! ... I mean Yes! WHAT?"
I’ll put 'maybe.' ~ Bloom County

Related Linux commands

case - Conditionally perform a command.
eval - Evaluate several commands/arguments.
expr - Evaluate expressions.
for - Expand words, and execute commands.
select - Accept user choices via keyboard input
test - Evaluate a conditional expression.
until - Execute commands (until error).
while - Execute commands.
File operators -f
Equivalent Windows command: IF - Conditionally perform a command.

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