Choose Function

Source

Choose

An alias function that will pick a random line (or lines) out of a text file.

The Function Declaration

Our alias function (choose) takes one required argument that we'll assign to the variable filename and one optional argument lines to indicate the number of lines to pull.

function choose -d "Random line from a file." --argument-names filename lines

The Error String

I'm setting a string-format variable that I'll use to color error messages in bold red.

set ERROR "\x1b[31;1m\t%s\n\n\x1b[0m"

See this stack overflow answer for more explanation of the codes. Basically the 31;1m part turns on red (31) and bold (1) and 0m resets it back to unbolded black text.

The Okay Variable

This is getting a little convoluted but I added another check for the second argument to make sure it's a number so this flag is just there to indicate that it did or didn't look like right.

set OKAY 0

I'm setting it to False so that it has to pass the checks in order to be unset.

Check the Number of Lines

Unlike random, shuf will let you pick multiple lines so I added a second (optional) argument to indicate the number of lines to output. If none is passed in then it's set to one, if something other than an integer is passed in then we'll set a flag so we know to skip calling the shuf command later on.

  • test -n "$lines" will return True if lines is non-empty so I negated it with ! to return True if it's empty.
if ! test -n "$lines"
  set lines 1
  set OKAY 1
else if ! test (string match --regex "^[0-9]+\$" $lines)
  set OKAY 0
  printf $ERROR "Not a valid number of lines: '$lines'"
else
  set OKAY 1
end

If It's a Text File, Use It

We'll be grabbing a line using the shuf command. shuf will hang if no filename is given and it will try and read binary files so first we have to test the filename to make sure it's a text file.

To do the check I'm using the file command which will have the word "text" in the output if we give it a text file. Then I feed the output from file to the string match command. This command defaults to only return true if the whole string matches so I added a glob to both ends of the "text" string to match any string that contains it. So, in order to pass the test filename has to have the name of a text file or we won't match the output of the file command.

First, though, we check if the lines argument was okay and if it was and filename passes its test then we can feed it to shuf.

if test $OKAY -ne 0; and test (string match "*text*" (file "$filename"))
   shuf -n $lines $filename
  • test $OKAY -ne 0 will return True if OKAY != 0. It will return an error if OKAY holds something other than a number.
  • the ; and syntax is a short-circuit syntax that won't run the second test if the first one fails.

Handle the Errors

If the number of lines wasn't okay or the filename wasn't valid then we'll emit a help message. Since we emitted any error message about the number

else
  if ! test -n "$filename"
    printf $ERROR  "**Missing Filename**"
  else if test $OKAY -ne 0
    printf $ERROR "Invalid File: '$filename'"
  end
  set OKAY 0
end # check filename

Emit a Help Message

If it had a valid number of lines and a valid filename then OKAY will have a value of 1, otherwise it will have a value of 0 and we'll emit the help message.

if test $OKAY -eq 0     
  printf "\t%s\n" \
         "Output a random line or lines from a text file." \ \
         "Usage:" \ \
         "    choose <filename> [<number of lines>]"
end # help message

One Last Thing

If the user passes in a flag as a filename this will get passed to the file command and in some cases this will cause it to emit a help message which will get passed to the shuf command. It's probably not a good idea to let that happen, but this was only supposed to be an alias so I wouldn't have to remember the syntax for shuf, so hopefully it'll work okay.

Sources