unix shell script variable declaration - command not found

Question

nOption=' | awk '{total+=$1} END {print total/1024"kb"}' '
find . -type f -printf "%s %p/n"| sort -nr | head -n10 $nOption

I would like to create a script to find the biggest file at current directory. This is my script, there had a error if I use the variable to substitute....

the output : ./big.sh: line 67: +=: command not found

but it works if i do not use variable :

find . -type f -printf "%s %p/n"| sort -nr | head -n10 | awk '{total+=$1} END {print total/1024"kb"}'

the output is what should i want: 680.021kb

What's wrong of my script??

thank you

Read I'm trying to put a command in a variable, but the complex cases always fail!. — chepner
– chepner, Commented Apr 25, 2014 at 12:04

l0b0 · Accepted Answer · 2014-04-25 12:05:12Z

4

Single quoted strings cannot contain other single quotes, so that awk command is interpreted as a shell command instead. Putting commands in variables is tricky, and in general it's easier, safer and more readable to create a function:

nOption() {
    awk '{total+=$1} END {print total/1024"kb"}'
}
find . -type f -printf "%s %p/n"| sort -nr | head -n10 | nOption

For this specific case, as @chepner points out, the issue is that you can't put command separators such as | in a string and then execute that as part of a pipe (without eval, which is evil).

edited Apr 25, 2014 at 12:05

answered Apr 25, 2014 at 8:52

l0b0

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1 Comment

chepner Over a year ago

Right answer, but the real problem, even if quoting were done correctly, is that you can't put shell syntax in a parameter like the OP tried. noption="| awk '...'" (with proper quoting and escaping in the awk script itself) would still fail, because the | would be treated as a literal character and therefore just another argument to head.

MarcoS · Accepted Answer · 2014-04-25 09:23:15Z

0

The problem is with quotes inside quotes, in variable expansion...
Why don't go with a one-liner? It's a (tiny) bit faster, and sleeker... :-)

find . -type f -printf "%s %p/n"| sort -nr | head -n10 | awk '{total+=$1} END {print total/1024"kb"}'

Update:
To make the script more flexible, you could do:

dir="."
units="1024"
unitsstring="kb"
find "$dir" -type f -printf "%s %p/n"| sort -nr | head -n10 | awk '{total+=$1} END {print total/$units"$unitsstring"}'

edited Apr 25, 2014 at 9:23

answered Apr 25, 2014 at 8:38

MarcoS

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2 Comments

YOHO Over a year ago

thank you. It is because this is a part of my script, I would like to change the nOption at some situation.

MarcoS Over a year ago

I see. But I think it's not possible to expand a variable ($1) inside a variable ($nOption). Flexibility is not obtained putting a command inside a variable, usually... You should select which parts of your command (string "kb", for example?) could change, in the future, and put these inside variables... See my updated answer to see an example... See also l0b0's answer, it's a different approach...

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