determining file type using a shell script

Question

Having trouble with this problem, i could use some help ....

create a shell script, fileType.sh, that takes a single command line parameter, a file path (might be relative or absolute). The script should examine that file and print a single line consisting of the phrase

Windows ASCII

if the files is an ASCII text file with CR/LF line terminators, or

Something else

if the file is binary or ASCII with “Unix” LF line terminators.

For example:

% ./fileType.sh ~cs252/Assignments/ftpAsst/d3.dat
Windows ASCII
% ./fileType.sh /bin/cat
Something else
% ./fileType.sh fileType.sh
Something else
% ./fileType.sh /usr/share/dict/words
Something else
%

Your script should not produce any other output when given a legal path to an existing file. (It may produce anything you like if given an incorrect path to a non-existent file.)

If the output of the file command contains the phrase “ASCII text” and the phrase “CRLF”, then the file is Windows ASCII text.

New to Unix; I have some C++ experience.

This is what I have in my script.

#!/bin/sh
line='file -b "$1"`

win=o
for i in $line; do
    if test `expr match "$1" "CRFL" | expr match "$1" "ASCII"` -gt 0 ; then
            win =1
            break
    fi
done

if test "$win" -eq 1; then
      printf "Windows ASCII\n"
else
      printf "Something else\n"
fi

I am using tcsh and basically I am trying to search for two varribles at the same time. In C++ I would use the "&&" operator. I don't know if unix has such an operator so I have tried to "pipe" them together.... with no luck.

I am getting "Something else" when I should be getting "Windows ASCII"

Eerily similar to stackoverflow.com/questions/27459148/… but definitely a better question. — tripleee
– tripleee, Commented Dec 13, 2014 at 20:05
Note that your script is a Bourne-shell style script, not a tcsh script, so your tagging is inaccurate since the problem is not the shell you run your commands from but the shell that runs this script. The use of the | in the if is dubious; test doesn't generate output on standard output and expr doesn't read anything from standard input. You may be thinking of the || operator. Using $1 instead of $i in the tests is also probably a mistake. Consider using the case operator too. — Jonathan Leffler
– Jonathan Leffler, Commented Dec 13, 2014 at 20:09
The | is part of the command substitution that provides the arguments for test (which would be easier to see if the OP weren't using backquotes rather than $(...)). — chepner
– chepner, Commented Dec 14, 2014 at 16:21

tripleee · Accepted Answer · 2014-12-13 20:26:16Z

1

You have some odd quoting and spelling errors in your script. Here is a fixed version.

#!/bin/sh
line=`file -b "$1"`  # backticks fixed

win=o
for i in $line; do  # fixed CRLF pro CRFL; fix bogus expr | expr
    if test `expr match "$1" "CRLF"` -gt 0 || test `expr match "$1" "ASCII"` -gt 0 ; then
            win=1   # cannot have space before equals sign
            break
    fi
done

if test "$win" -eq 1; then
      printf "Windows ASCII\n"
else
      printf "Something else\n"
fi

An immediate improvement would be to avoid expr, and to use the modern syntax for process substitution -- $(file ...) instead of `file ...` as well as fold the multiple conditionals into a single case statement. This also avoids the loop over the tokens in line which seems rather unidiomatic and wasteful.

#!/bin/sh
case $(file -b "$1") in
    # I guess the message has ASCII before CRLF always, but cover all bases
    *CRLF*ASCII* | *ASCII*CRLF*)
        echo "Windows ASCII" ;;
    *)
        echo "Something else" ;;
esac

edited Dec 13, 2014 at 20:26

answered Dec 13, 2014 at 20:20

tripleee

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2 Comments

Byrn Over a year ago

both of those solutions appear to work but when I submit it, the auto checker says it fails to read a .cpp file ... Failed when running: ./fileType.sh 'aardavark.cpp'

tripleee Over a year ago

Without access to this test file, it's hard to tell what could cause it. Do you have any additional information?

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