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commands:builtin:mapfile [2012/03/08 08:47] ormaaj [The callback] read + mapfile combination. |
commands:builtin:mapfile [2013/08/19 08:09] (current) ormaaj [Bugs] |
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| ====== The mapfile builtin command ====== | ====== The mapfile builtin command ====== | ||
| - | :V4: | ||
| ===== Synopsis ===== | ===== Synopsis ===== | ||
| Line 89: | Line 88: | ||
| </code> | </code> | ||
| - | This example based upon yet another #bash question illustrates mapfile in combination with read. The sample input is the heredoc to ''main''. The goal is to build a "struct" based upon records in the input file made up from the numbers following the colon on each line. Every 3rd line is a key followed by 2 corresponding fields. The showRecord function takes a key and returns the record. | + | This example based on yet another #bash question illustrates mapfile in combination with read. The sample input is the heredoc to ''main''. The goal is to build a "struct" based upon records in the input file made up of the numbers following the colon on each line. Every 3rd line is a key followed by 2 corresponding fields. The showRecord function takes a key and returns the record. |
| - | <code>#!/usr/bin/env bash | + | |
| + | <code> | ||
| + | #!/usr/bin/env bash | ||
| showRecord() { | showRecord() { | ||
| Line 97: | Line 98: | ||
| parseRecords() { | parseRecords() { | ||
| + | trap 'unset -f _f' RETURN | ||
| _f() { | _f() { | ||
| local x | local x | ||
| IFS=: read -r _ x | IFS=: read -r _ x | ||
| - | keys[x]=n++ | + | ((keys[x]=n++)) |
| } | } | ||
| - | + | local n | |
| - | trap 'unset -f _f' RETURN | + | |
| - | local -i n | + | |
| _f | _f | ||
| - | mapfile -tc2 -C _f vals | + | mapfile -tc2 -C _f "$1" |
| - | vals=("${vals[@]##*:}") | + | eval "$1"'=("${'"$1"'[@]##*:}")' # Return the array with some modification |
| } | } | ||
| main() { | main() { | ||
| - | local -ai keys | + | local -a keys vals |
| - | parseRecords | + | parseRecords vals |
| showRecord "$1" | showRecord "$1" | ||
| } | } | ||
| - | main "$@" <<-"EOF" | + | main "$1" <<-"EOF" |
| fabric.domain:123 | fabric.domain:123 | ||
| routex:1 | routex:1 | ||
| Line 124: | Line 124: | ||
| routex:6 | routex:6 | ||
| routey:4 | routey:4 | ||
| - | EOF</code> | + | EOF |
| + | </code> | ||
| - | For example, running "scriptname 321" would output "key[321] = 6, 4". Every 2 lines mapfile reads, the function _f is called which reads one line. Since the first line in the file is a key, and _f is responsible for the keys, it gets called once before mapfile so that mapfile starts reading the second line of input, calling _f with each subsequent 2 iterations. The RETURN trap is nothing to worry about, its just how I implement "private methods" in Bash. | + | For example, running ''scriptname 321'' would output ''key[321] = 6, 4''. Every 2 lines read by ''mapfile'', the function ''_f'' is called, which reads one additional line. Since the first line in the file is a key, and ''_f'' is responsible for the keys, it gets called first so that ''mapfile'' starts by reading the second line of input, calling ''_f'' with each subsequent 2 iterations. The RETURN trap is unimportant. |
| ===== Bugs ===== | ===== Bugs ===== | ||
| - | * Early implementations were buggy. For example, ''mapfile'' filling the readline history buffer with calls to the ''CALLBACK''. This was fixed in 4.1 beta. Some bugs may still exist. | + | * Early implementations were buggy. For example, ''mapfile'' filling the readline history buffer with calls to the ''CALLBACK''. This was fixed in 4.1 beta. |
| + | * ''mapfile -n'' reads an extra line beyond the last line assigned to the array, through Bash. [[ftp://ftp.gnu.org/gnu/bash/bash-4.2-patches/bash42-035 | Fixed in 4.2.35]]. | ||
| + | * ''mapfile'' callbacks could cause a crash if the variable being assigned is manipulated in certain ways. [[https://lists.gnu.org/archive/html/bug-bash/2013-01/msg00039.html]]. Fixed in 4.3. | ||
| ===== To Do ===== | ===== To Do ===== | ||
| * Create an implementation as a shell function that's portable between Ksh, Zsh, and Bash (and possibly other bourne-like shells with array support). | * Create an implementation as a shell function that's portable between Ksh, Zsh, and Bash (and possibly other bourne-like shells with array support). | ||