# The if-clause

## Synopsis

    if <LIST>; then
      <LIST>
    fi

    if <LIST>; then
      <LIST>
    else
      <LIST>
    fi

    if <LIST>; then
      <LIST>
    elif <LIST>; then
      <LIST>
    else
      <LIST>
    fi

## Description

The `if`-clause can control the script's flow (what's executed) by
looking at the exit codes of other commands.

All commandsets `<LIST>` are interpreted as [command
lists](../../syntax/basicgrammar.md#lists), thus they can contain the whole
palette from [simple commands](../../syntax/basicgrammar.md#simple_commands)
over [pipelines](../../syntax/basicgrammar.md#pipelines) to [compound
commands](../../syntax/basicgrammar.md#compound_commands) (and their
combination) as condition.

### Operation

The **`if <LIST>`** commands are executed. If the exit code was 0 (TRUE)
then the **`then <LIST>`** commands are executed, otherwise the
**`elif <LIST>`** commands and their **`then <LIST>`** statements are
executed in turn, if all down to the last one fails, the
**`else <LIST>`** commands are executed, if one of the `elif` succeeds,
its `then` thread is executed, and the `if`-clause finishes.

Basically, the `elif` clauses are just additional conditions to test
(like a chain of conditions) if the very first condition failed. If one
of the conditions fails, the `else` commands are executed, otherwise the
commands of the condition that succeeded.

## Examples

**Check if a specific user exists in /etc/passwd :-)**

    if grep ^myuser: /etc/passwd >/dev/null 2>&1; then
      echo "Yes, it seems I'm real"
    else
      echo "Uh - am I a ghost?"
    fi

**Mount with check**

    if ! mount /mnt/backup >/dev/null 2>&1; then
      echo "FATAL: backup mount failed" >&2
      exit 1
    fi

**Multiple commands as condition**

It's perfectly valid to do:

    if echo "I'm testing!"; [ -e /some/file ]; then
      ...
    fi

The exit code that dictates the condition's value is the exit code of
the very last command executed in the condition-list (here: The
`[ -e /some/file ]`)

**A complete pipe as condition**

A complete pipe can also be used as condition. It's very similar to the
example above (multiple commands):

    if echo "Hello world!" | grep -i hello >/dev/null 2>&1; then
      echo "You just said 'hello', yeah?"
    fi

## Portability considerations

## See also

-   Internal: [the classic test command](../../commands/classictest.md)