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94 lines
2.3 KiB
Markdown
94 lines
2.3 KiB
Markdown
# Generate code with own arguments properly quoted
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---- dataentry snipplet ---- snipplet_tags: arguments, quoting,
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escaping, wrapper LastUpdate_dt: 2010-07-31 Contributors: Jan Schampera
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type: snipplet
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------------------------------------------------------------------------
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Keywords: arguments,escape,quote,wrapper,generate
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-------------- -----------------------------------------
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Contributor: self
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There are situations where Bash code needs to generate Bash code. A
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script that writes out another script the user or cron may start, for
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example.
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The general issue is easy, just write out text to the file.
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A specific detail of it is tricky: If the generated script needs to call
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a command using the arguments the first original script got, you have
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problem in writing out the correct code.
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I.e. if you run your generator script like
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./myscript "give me 'some' water"
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then this script should generate code that looks like
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echo give me 'some' water"
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you need correct escapes or quotes to not generate shell special
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characters out of normal text (like embedded dollar signs `$`).
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**[Solution:]{.underline}**
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A loop over the own arguments that writes out properly quoted/escaped
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code to the generated script file
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There are two (maybe more) easy options:
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- writing out singlequoted strings and handle the embedded
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singlequotes
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- the [printf command](../commands/builtin/printf.md) knows the `%q` format
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specification, which will print a string (like `%s` does), but with
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all shell special characters escaped
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## Using singlequoted string
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#!/bin/bash
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# first option:
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# generate singlequoted strings out of your own arguments and handle embedded singlequotes
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# here to call 'echo' in the generated script
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{
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printf "#!/bin/bash\n\n"
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printf "echo "
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for arg; do
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arg=${arg/\'/\'\\\'\'}
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printf "'%s' " "${arg}"
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done
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printf "\n"
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} >s2
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The generated script will look like:
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#!/bin/bash
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echo 'fir$t' 'seco "ond"' 'thir'\''d'
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## Using printf
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The second method is easier, though more or less Bash-only (due to the
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`%q` in printf):
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#!/bin/bash
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{
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printf "#!/bin/bash\n\n"
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printf "echo "
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for arg; do
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printf '%q ' "$arg"
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done
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printf "\n"
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} >s2
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The generated script will look like:
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#!/bin/bash
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echo fir\$t seco\ \"ond\" thir\'d
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