I have an awk script that I have defined thus:
#!/usr/bin/env awk BEGIN { if (!len) len = 1; end = start + len } { for (i = start; i < end; i++) { print $1 } } I have saved it as columns and chmod +x'd it. I want invoke it so that start and end are defined as it traverses over a file. I was thinking this should work:
cat some_file | columns -v start=2 But it doesn't. Help!
Try using:
#!/usr/bin/awk -f as an interpreter
awk is hard-coded - of necessity, due to having to make do with one argument - this should work on all modern Unix platforms. (Do tell if you know of any where it doesn't.)-S is non POSIX compliant :(#!/usr/bin/env awk -f may work for you (works on OS X, for instance, but not on Linux).env is the easiest way to handle this problem:
#!/usr/bin/env -S awk -f to add more options, and to ensure no interference with your arguments, and awk's arguments:
#!/usr/bin/env -S awk -F: -f ${_} -- BEGIN { # delete argv[1], which == ENVIRON[_] delete ARGV[1] } # rest of my awk program as env has a POSIX standard, this shbang should get you around the difficulties of non-standard shbang implementations across unixen.
EDIT
after having written this I realized that '-S' is a non-POSIX compliant FreeBSD env extension. So shell wrapper is probably the way to go, unfortunate as that is.
${_} relies on the _ environment variable being set by the shell from which you launched the script, and will not work if the script isn’t launched directly from a shell.Unfortunately, this is not easy to solve in a portable way. The standard technique looks like this (substitute /usr/bin/awk for your awk path):
#!/usr/bin/awk -f BEGIN { if (!len) len = 1; end = start + len } { for (i = start; i < end; i++) { print $1 } } The hard-coded awk path and non-standard -f flag, makes this not portable across all *nixes. If you are only ever going to run your script on one machine, then this may work fine. However, to make a portable awk script, you will need to wrap it in a shell script. Here are two ways that you can do it in one file:
The first way is standard and easy to read:
#!/bin/sh awk ' BEGIN { if (!len) len = 1; end = start + len } { for (i = start; i < end; i++) { print $1 } } ' "$@" Unfortunately, this falls short in two key ways:
' character, you will need to type it like this: '"'"' to "escape" it.Another solution, is to use sed to strip out the sh wrapper:
#!/bin/sh exec awk "$(sed '1,2d' "$0")" "$@" BEGIN { if (!len) len = 1; end = start + len } { for (i = start; i < end; i++) { print $1 } } This is something like a two line shabang header. It calls awk using the file from line 3 down as the script argument. This allows you to keep your pretty syntax highlighting and you can still use ' characters to your heart's content. The two downsides I see are:
Below is the answer for this problem -
#!/bin/awk -f 
mawk on /usr/bin/awk that does not support -f option.
Alternatively the awk script could be placed in a shell script with just the awk command inside:
#!/bin/sh awk 'BEGIN { if (!len) len = 1; end = start + len } { for (i = start; i < end; i++) { print $1 } }' <file> This avoids using awk in the shebang and provides the possibility to execute the awk script either as a simple shell script with
./script or sourcing it from the current shell (or a shell script) with
. script The latter option will avoid spawing a new shell and just executing the awk command.
