Bash Script - Invalid Arithmetic Operator

Question

with the below code I keep getting the following errors:

#!/bin/bash
    sourceFile="file1.log"
    targetFile="/etc/network/interfaces"
    numLines=$(wc -l ${sourceFile})
    if (( counter >= "$numLines" || ! -f "${sourceFile}" )); then
            echo "invaild file"
            exit 0
    fi
    while [ "$counter" -le "$numLines" ]; do
            sed -i "${2} s/.*/wireless-key s: $(sed -n "${counter}"p <<< "${sourceFile}")/" "${targetFile}"
            counter=$((counter + 1))
    done

with the above code I keep getting the following errors:

  > ./2test.sh: line 5: ((: counter >= 12 file1.log || ! -f file1.log : syntax error: invalid arithmetic operator (error token is ".log || !
  > -f file1.log ") ./2test.sh: line 9: [: : integer expression expected

wc -l ${sourceFile} prints 12 file1.log, so that's the value of $numLines. numLines="$(wc -l < "${sourceFile}")" should give you just the number (the quotes are free this week, enjoy). — Biffen
– Biffen, Commented Feb 19, 2017 at 13:33
Seems like echo 'invalid file' >&2; exit 1 would be more appropriate. Errors should be printed to stderr, and the script ought to return non-zero if it fails. — William Pursell
– William Pursell, Commented Feb 19, 2017 at 13:37
Also ! -f "${sourceFile}" is not valid code in (()), maybe try it in square brackets i.e (( counter >= "$numLines" )) || [[ ! -f "${sourceFile}" ]] — 123
– 123, Commented Feb 19, 2017 at 13:38
I've just got the last error still, do you know anything on that one? — spbr
– spbr, Commented Feb 19, 2017 at 13:50

Biffen · Accepted Answer · 2017-02-19 14:01:05Z

3

^{^{Turning my comment into an answer.}}

wc with an explicit filename includes that filename in the output, so:

wc -l ${sourceFile}

Prints:

12 file1.log

That's then the value of $numLines.

The clue is in the error message: It includes the expanded expression:

> ./2test.sh: line 5: ((: counter >= 12 file1.log || ! -f file1.log : syntax error[…]
                                     ^^^^^^^^^^^^

You can avoid getting that filename by redirecting the file's contents to wc instead:

numLines="$(wc -l < "${sourceFile}")"

^{(The added quotes are thrown in as it's a good habit. (No, they're not strictly necessary in this case.) (And yes, the qoutes are correct, even if SO's syntax highlighter doesn't quite seem to understand them.)}

There are other issues in the script (mentioned in the comments), but one question at a time. I will take the opportunity to recommend ShellCheck, though.

edited Feb 19, 2017 at 14:01

answered Feb 19, 2017 at 13:49

Biffen

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2 Comments

William Pursell Over a year ago

nit: "piping" the file's contents can be done with cat $sourceFile | wc -l (UUOC), but there is no pipe involved with wc -l < $sourceFile. A redirection is not a pipe.

Biffen Over a year ago

@WilliamPursell Heh, lazy me. Fixed. Thanks!

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