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syntax:ccmd:classic_for [2010/12/11 12:04] 127.0.0.1 external edit |
syntax:ccmd:classic_for [2017/01/19 21:02] (current) 4dummies [Loop over a number range] removed a stray "1" |
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| Line 13: | Line 13: | ||
| done | done | ||
| </code> | </code> | ||
| + | alternative, historical and undocumented syntax ((http://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xcu_chap02.html#tag_23_02_09_12)) | ||
| <code> | <code> | ||
| - | # alternative, historical and undocumented syntax | + | for <NAME>; { |
| - | + | ||
| - | for <NAME> { | + | |
| <LIST> | <LIST> | ||
| } | } | ||
| - | for <NAME> in <WORDS> { | + | for <NAME> in <WORDS>; { |
| <LIST> | <LIST> | ||
| } | } | ||
| Line 46: | Line 44: | ||
| } | } | ||
| </code> | </code> | ||
| - | 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). | + | 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). |
| Line 127: | Line 125: | ||
| done | done | ||
| </code> | </code> | ||
| + | |||
| + | ==== Loop over a number range ==== | ||
| + | |||
| + | Beginning in Bash 4, you can also use "sequence expression" form of [[syntax:expansion:brace|brace expansion]] syntax when looping over numbers, and this form does not create leading zeroes unless you ask for them: | ||
| + | |||
| + | <code bash> | ||
| + | # 100 numbers, no leading zeroes | ||
| + | for x in {0..99}; do | ||
| + | echo $x | ||
| + | done | ||
| + | </code> | ||
| + | |||
| + | <code bash> | ||
| + | # Every other number, width 3 | ||
| + | for x in {000..99..2}; do | ||
| + | echo $x | ||
| + | done | ||
| + | </code> | ||
| + | |||
| + | 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 ===== | ===== Portability considerations ===== | ||
| Line 133: | Line 151: | ||
| * [[syntax:ccmd:c_for]] | * [[syntax:ccmd:c_for]] | ||
| - | |||