bash-hackers-wiki/docs/syntax/ccmd/classic_for.md

# The classic for-loop

## Synopsis

    for <NAME>; do
      <LIST>
    done

    for <NAME> in <WORDS>; do
      <LIST>
    done

alternative, historical and undocumented syntax [^1]

    for <NAME>; {
      <LIST>
    }

    for <NAME> in <WORDS>; {
      <LIST>
    }

## Description

For every word in `<WORDS>`, one iteration of the loop is performed and
the variable `<NAME>` is set to the current word. If no "`in <WORDS>`"
is present to give an own word-list, then the positional parameters
(`"$@"`) are used (the arguments to the script or function). In this
case (and only in this case), the semicolon between the variable name
and the `do` is optional.

If you use the loop-variable inside the for-loop and it can contain
spaces, you need to quote it, since normal word-splitting procedures
apply.

:!: Like all loops (both `for`-loops, `while` and `until`), this loop
can be

-   terminated (broken) by the `break` command, optionally as `break N`
    to break `N` levels of nested loops
-   forced to immediately do the next iteration using the `continue`
    command, optionally as `continue N` analog to `break N`

Bash knows an alternative syntax for the `for` loop, enclosing the loop
body in `{...}` instead of `do ... done`:

``` bash
for x in 1 2 3
{
  echo $x
}
```

This syntax is **not documented** and should not be used. I found the
parser definitions for it in 1.x code, and in modern 4.x code. My guess
is that it's there for compatiblity reasons. This syntax is not
specified by POSIX(r).

### Return status

The return status is the one of the last command executed in `<LIST>` or
`0` (`TRUE`), if the item list `<WORDS>` evaluates to nothing (i.e.:
"is empty"!).

## Examples

### Iterate over array elements

With some array syntax (see [arrays](../../syntax/arrays.md)) you can easily
"feed" the for-loop to iterate over all elements in an array (by
mass-expanding all elements):

``` bash
for element in "${myarray[@]}"; do
  echo "Element: $element"
done
```

Another way is to mass-expand all used indexes and access the array by
index:

``` bash
for index in "${!myarray[@]}"; do
  echo "Element[$index]: ${myarray[$index]}"
done
```

### List positional parameters

You can use this
[function](../../syntax/basicgrammar.md#shell_function_definitions) to test how
arguments to a command will be interpreted and parsed, and finally used:

``` bash
argtest() {
  n=1
  for arg; do
    echo "Argument $((n++)): \"$arg\""
  done
}
```

### Loop through a directory

Since pathname expansion will expand all filenames to separate words,
regardless of spaces, you can use the for-loop to iterate through
filenames in a directory:

``` bash
for fn in *; do
  if [ -h "$fn" ]; then
    echo -n "Symlink: "
  elif [ -d "$fn" ]; then
    echo -n "Dir: "
  elif [ -f "$fn" ]; then
    echo -n "File: "
  else
    echo -n "Unknown: "
  fi
  echo "$fn"
done
```

Stupid example, I know ;-)

### Loop over lines of output

To be complete: You can change the internal field separator (IFS) to a
newline and thus make a for-loop iterating over lines instead of words:

``` bash
IFS=$'\n'
for f in $(ls); do
  echo $f
done
```

This is just an example. In *general*

-   it's not a good idea to parse `ls(1)` output
-   the [while loop](../../syntax/ccmd/while_loop.md) (using the `read` command)
    is a better joice to iterate over lines

### Nested for-loops

It's of course possible to use another for-loop as `<LIST>`. Here,
counting from 0 to 99 in a weird way:

``` bash
for x in 0 1 2 3 4 5 6 7 8 9; do
  for y in 0 1 2 3 4 5 6 7 8 9; do
    echo $x$y
  done
done
```

### Loop over a number range

Beginning in Bash 4, you can also use "sequence expression" form of
[brace expansion](../../syntax/expansion/brace.md) syntax when looping over
numbers, and this form does not create leading zeroes unless you ask for
them:

``` bash
# 100 numbers, no leading zeroes
for x in {0..99}; do
  echo $x
done
```

``` bash
# Every other number, width 3
for x in {000..99..2}; do
  echo $x
done
```

WARNING: the entire list is created before looping starts. If your list
is huge this may be an issue, but no more so than for a glob that
expands to a huge list.

## Portability considerations

## See also

-   [c_for](../../syntax/ccmd/c_for.md)

[^1]: <http://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xcu_chap02.html#tag_23_02_09_12>