Substrings in shell script

Question

Am trying to get a substring from a string but am getting the error: ${curr_rec:3:4}: bad substitution

#!/bin/ksh

get_file_totals()
{

    if [ -e "$file_name" ]
    then
        IFS=''
        while read line
        do
        curr_rec=$line
        echo ${curr_rec:3:4}
        done < "$file_name"
    else

        echo "error"
    fi
}

file_name="$1"
get_file_totals

FWIW I get this error if I (wrongly) call the script like `sh myscript`. I can't reproduce it otherwise. — roaima, May 27 '15 at 10:06
You may want to read [Why is using a shell loop to process text considered bad practice?](http://unix.stackexchange.com/q/169716). You've fallen in almost every trap there. — Stéphane Chazelas, May 27 '15 at 10:54

score 3 · Answer 1 · answered May 27 '15 at 10:03

3

You're invoking ksh. The kind of substitution you are wanting to do works only since ksh '93. Is there a chance you are using an older version? Run ksh and check for the existence of KSH_VERSION. If it doesn't exist or is before '93, it's too old.

answered May 27 '15 at 10:03

Otheus

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That syntax is also available in `zsh`'s `ksh` and `mksh` since version 30.1 (2007). – Stéphane Chazelas May 27 '15 at 10:58
(with mksh, you need the `-U` option for `${var:offset:length}` to work with characters as opposed to bytes in UTF-8 locales). – Stéphane Chazelas May 27 '15 at 11:20

score 1 · Accepted Answer · answered May 27 '15 at 11:31

It would be more efficient to rewrite this, thereby avoiding the issue in the first place:

#!/bin/ksh

get_file_totals()
{

    if [ -e "$file_name" ]
    then
        cut -c4-7 "$file_name"
    else
        echo "error"    # consider stderr by appending >&2
    fi
}

file_name="$1"
get_file_totals

Substrings in shell script

2 Answers2