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55 lines
2.4 KiB
Text
55 lines
2.4 KiB
Text
COMMENT(!MOD!zsh/mapfile
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Access to external files via a special associative array.
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!MOD!)
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cindex(parameter, file access via)
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The tt(zsh/mapfile) module provides one special associative array parameter of
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the same name.
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startitem()
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vindex(mapfile)
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item(tt(mapfile))(
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This associative array takes as keys the names of files; the resulting
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value is the content of the file. The value is treated identically to any
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other text coming from a parameter. The value may also be assigned to, in
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which case the file in question is written (whether or not it originally
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existed); or an element may be unset, which will delete the file in
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question. For example, `tt(vared mapfile[myfile])' works as expected,
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editing the file `tt(myfile)'.
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When the array is accessed as a whole, the keys are the names of files in
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the current directory, and the values are empty (to save a huge overhead in
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memory). Thus tt(${(k)mapfile}) has the same affect as the glob operator
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tt(*(D)), since files beginning with a dot are not special. Care must be
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taken with expressions such as tt(rm ${(k)mapfile}), which will delete
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every file in the current directory without the usual `tt(rm *)' test.
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The parameter tt(mapfile) may be made read-only; in that case, files
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referenced may not be written or deleted.
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A file may conveniently be read into an array as one line per element
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with the form
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`var(array)tt(=LPAR()"${(f)mapfile[)var(filename)tt(]}"RPAR())'.
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The double quotes are necessary to prevent empty lines from being
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removed.
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)
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enditem()
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subsect(Limitations)
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Although reading and writing of the file in question is efficiently
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handled, zsh's internal memory management may be arbitrarily baroque;
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however, tt(mapfile) is usually very much more efficient than
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anything involving a loop. Note in particular that
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the whole contents of the file will always reside physically in memory when
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accessed (possibly multiple times, due to standard parameter substitution
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operations). In particular, this means handling of sufficiently long files
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(greater than the machine's swap space, or than the range of the pointer
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type) will be incorrect.
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No errors are printed or flagged for non-existent, unreadable, or
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unwritable files, as the parameter mechanism is too low in the shell
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execution hierarchy to make this convenient.
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It is unfortunate that the mechanism for loading modules does not yet allow
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the user to specify the name of the shell parameter to be given the special
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behaviour.
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