Bash script error for syntax operand expected "="

Question

I get an error in my Bash shell script script.sh on this line of code:

let initialLines=$(grep '' "1ドル" | wc -l || true)

error is: script.sh: line 146: let: initialLines=: syntax error: operand expected (error token is "=")

What is syntactically incorrect here?

• chepner: Not an error, but since every string will match the empty regular expression, your grep command is equivalent to cat "1ドル", in which case you could simply run wc -l "1ドル".
• mklement0: @chepner: Good point, but it should be wc -l < "1ドル" (note the <), so as to prevent wc from outputting the input filename as well.
• chepner: @mklement0 Details, details :) I suspect the the regular expression is wrong anyway, which means the pipeline is still relevant. (Although grep -c could be used instead as well.)

Answer 1

tl;dr:

Double-quote your command substitution:

let initialLines="$(grep '' "1ドル" | wc -l || true)"

That said, as explained in chepner's helpful answer, you could just use a simple assignment without needing to double-quote the RHS, although to get the same outcome as with let here, be sure to declare the variable with -i first; e.g., declare -i initialLines

---

It looks like the RHS of your assignment - the command substitution ($(...)) - evaluates either to the empty string or a whitespace-prefixed string in the course of the shell expansions that happen before the command is executed, so that bash ends up trying to parse one of the following commands:

let initialLines=
let initialLines= 2

If you try these in isolation, you'll get the syntax error you've experienced.

---

The most likely explanation is that you're using BSD wc, such as on macOS, which outputs the line count requested with -l with leading whitespace.

---

A simple fix is to double-quote the command substitution:

let initialLines="$(grep '' "1ドル" | wc -l || true)"

---

As for the command in your command substitution (it may just be an example, but it's worth commenting on):

• grep '' will always return all input lines, so it's nothing more than a less efficient cat.

• There is no point in using || true:

  • The exit code of the subshell in which the command substitution runs is not relevant, even with set -e in effect.

  • Also, by using true as the alternative command, you'll break the let command as well, because builtin true has no stdout output.

• In summary, your entire command substitution could be reduced to wc -l < "1ドル".

• Chisx: Yes this did get rid of the error and I am using macOS so very knowledgeable answer

Answer 2

There is little or no need to use the let command here.

initialLines=$(grep '' "1ドル" | wc -l)

This solves the problem (the command substitution producing an empty or white-space prefixed string) pointed out by @mklement0 in a different way; unlike the argument to the let command, the value on the right-hand side of an assignment is not subject to word-splitting.

• mklement0: While good advice in general, there is a subtlety to consider here: to really make the two commands equivalent, you must declare initialLines with -i first, otherwise just initialLines=$(grep '' "1ドル" | wc -l) will retain leading whitespace, such as the one output by wc -l on macOS.