Pass CAT command as argument to function - bash

Question

I'm trying to write a very simple bash script that modifies a number of files, and I'm outputting the results of each command to a log as a check whether the command was completed successfully. Everything appears to be working except I can't pass CAT with variables to my script -- I keep getting a cat: >>: No such file or directory error.
#! /bin/bash
file1="./file1"
file2="./file2"
check () {
if ( $1 > /dev/null ) then
echo " $1 : completed" | tee -a log
return 0;
else
echo "ERR> $1 : command failed" | tee -a log
return 1;
fi
}
check "cp $file1 $file1.bak" # this works fine
check "sed -i s/text/newtext/g $file1" # this works, too
check "cat $file1 >> $file2" # this does not work
I've tried any number of combinations of quoting the command. The only way that I can get it to work is by using the following:
check $(cat $file1 >> $file2)
However, this does not pass the command itself to check only the return value, so $1 in function check carries /dev/null and not the command performed, which is not the particular behaviour I want.
Just for completeness, the log file looks like:
cp ./file1 ./file1.bak : completed
sed -i s/text/newtext/g ./file1 : completed
ERR> cat ./file1 >> ./file2 : command failed
I'm sure the solution is rather simple, but it has eluded me for a few hours and no amount of Google searches has yielded any help. Thanks for having a look.

Answer 1

The problem is that the I/O redirection in your cat command is not being interpreted as I/O redirection but rather as a simple argument to the cat command. It's not cat so much as the I/O redirection that is causing grief. Trying a pipeline would also give you problems.
Options available to remedy this include:
check "cp $file1 $file2" # Use copy instead of cat and I/O redirection; clobbers file2
check "eval cat $file1 >> $file2" # Use eval to handle I/O redirection, piping, etc
If either $file1 or $file2 contains shell special characters, the eval option is dangerous.
The cp command substitutes something that works without needing I/O redirection. You could even use a (microscopic) shell script to handle the job — where your script executes the shell script, and the shell script handles the redirection:
#!/bin/sh
exec cat ${1:?} >> ${2:?}
This generates a default error message if either argument 1 or 2 is missing (but doesn't object to extra arguments).

Answer 2

EDIT: the approach I first tried below doesn't quite work. There's another trick that can rescue this, even without resorting to bash magic, but it's getting ugly.
The >> redirection occurs at the wrong level, in this case. You wind up asking cat to read ./file, then a file named >>, then ./file2. To get the redirection to occur you'll need to do it elsewhere (see below), or invoke eval.
I'd recommend not using eval, but instead, rejiggering the logic of function check instead. You can redirect check at the top level, e.g.,:
check() {
if "$#"; then
echo " $# : completed" | tee -a log
return 0
fi
echo "ERR> $# : failed, status $?" | tee -a log
return 1
}
check cp "$file1" "$file.bak" # doesn't print anything
check sed -i s/text/newtext/g "$file1" >/dev/null # does print, so >/dev/null
check cat "$file1" >> "$file2"
(The double quotes here in the invocations of check are in case file1 and/or file2 ever acquire meta-characters like * or ;, or white space, etc.)
EDIT: as #cdm and #rici note, this fails for the append-to-file cases, because check's output is redirected even for the tee command. Again the redirection is happening at the wrong level. It's possible to fix this by adding another level of indirection:
append_to_file() {
local fname
fname="$1"
shift
"$#" >> "$fname"
}
check cp "$file1" "$file.bak"
check append_to_file /dev/null sed -e s/text/newtext/g "$file1"
check append_to_file "$file2" cat "$file1"
Now, though, the completed and failure messages log append_to_file at the front, which is really pretty klunky. I think I'd go back to eval instead.