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# ☑ Bash expansion weirdness

25 Jan 2013 at 11:12AM in Software
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Expanding a substring of “$*” in bash seems to magically add command-line parameter zero. Here’s a quirky one. In the bash shell, "$*" expands to a single string which is a whitespace-separated list of arguments starting at one. So if you have the following script as script.sh:

 1 2 #!/bin/bash echo Arguments: "$*"  … and you call it as script.sh arg1 arg2 arg3 then you’ll get the following output: Arguments: arg1 arg2 arg3  So far so tedious. However, if we use some of bash’s parameter expansion rules to select a substring (in this case the substring starting at zero, or the whole string in fact):  1 2 #!/bin/bash echo Arguments: "${*:0}" 

… then suddenly you get parameter zero (the filename of the script) included:

Arguments: ./script.sh arg1 arg2 arg3


I’m not sure if that’s a bug or I’m missing some subtlety and it’s expected behaviour, but it’s one of those issues that’s pretty tough to Google around so I suspect it’ll remain a mystery.

25 Jan 2013 at 11:12AM in Software
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Photo by Vicko Mozara
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