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Sometimes I have a one-liner that I am repeating many times for a particular task, but will likely never use again in the exact same form. It includes a file name that I am pasting in from a directory listing. Somewhere in between and creating a bash script I thought maybe I could just create a one-liner function at the command line like:

numresults(){ ls "$1"/RealignerTargetCreator | wc -l }

I've tried a few things like using eval, using numresults=function..., but haven't stumbled on the right syntax, and haven't found anything on the web so far. (Everything coming up is just tutorials on bash functions).

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2
  • tell me the number of files in the directory $1/RealignerTargetCreator. Commented Feb 17, 2016 at 19:38
  • 3
    you re missing the semicolon at the end. ... ; } Commented Mar 29, 2018 at 12:09

5 Answers 5

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43

Quoting my answer for a similar question on Ask Ubuntu:

Functions in bash are essentially named compound commands (or code blocks). From man bash:

Compound Commands
   A compound command is one of the following:
   ...
   { list; }
          list  is simply executed in the current shell environment.  list
          must be terminated with a newline or semicolon.  This  is  known
          as  a  group  command. 

...
Shell Function Definitions
   A shell function is an object that is called like a simple command  and
   executes  a  compound  command with a new set of positional parameters.
   ... [C]ommand is usually a list of commands between { and },  but
   may  be  any command listed under Compound Commands above.

There's no reason given, it's just the syntax.

Try with a semicolon after wc -l:

numresults(){ ls "$1"/RealignerTargetCreator | wc -l; }
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7 Comments

Well, that was simple! (I mean the semicolon). Again, its always good to get a deeper understanding of how the shell works.
The semicolon is necessary because } is not a control character and does not terminate a command. Notice echo } simply outputs the literal string.
@chepner That's just pushing the question one level down. Those who created the grammar could make } special for functions. zsh, for example, has no problems with foo () {echo foo}.
I'm describing what is, not what could be.
@chepner And I'm saying it isn't necessary, it's just the way the syntax is.
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4

Don't use ls | wc -l as it may give you wrong results if file names have newlines in it. You can use this function instead:

numresults() { find "$1" -mindepth 1 -printf '.' | wc -c; }
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3 Comments

Thanks. It's always good to deepen one's bash skills! Just curious, how could a file name have a newline in it?
You can use touch $'file\nwith\nline' to create a filename with newlines
@abalter Yep. That's why it's a mantra: Don't parse ls output.
4

You can get a 

bash: syntax error near unexpected token `('

error if you already have an alias with the same name as the function you're trying to define.

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3

You can also count files without find. Using arrays,

numresults () { local files=( "$1"/* ); echo "${#files[@]}"; }

or using positional parameters

numresults () { set -- "$1"/*; echo "$#"; }

To match hidden files as well,

numresults () { local files=( "$1"/* "$1"/.* ); echo $(("${#files[@]}" - 2)); }
numresults () { set -- "$1"/* "$1"/.*; echo $(("$#" - 2)); }

(Subtracting 2 from the result compensates for . and ...)

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2 Comments

The first of the hidden files functions could use dotglob, since it's using arrays anyway.
Hm, for some reason I remembered dotglob matching . and .. as well, but it doesn't.
-3

The easiest way maybe is echoing what you want to get back.

function myfunc()
{
    local  myresult='some value'
    echo "$myresult"
}

result=$(myfunc)   # or result=`myfunc`
echo $result

Anyway here you can find a good how-to for more advanced purposes

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