Loop Over Files in tcsh Shell - Command Line Tips

[ehrenfest]

Is it possible to do a for loop at the command line over all files in a given directory using the tcsh shell? I want to loop over all files and apply some commands (e.g. sed) to each one.

EDIT: I called it a "for" loop because I saw a "for" command when I googled this problem but of course I just want to loop over all the files

 

[D H]

Yes. It's called foreach.

This will invoke the command 'do_something_to' on each .c file in the current directory:

foreach f (*.c)
   do_something_to $f
end

I often use foreach in conjunction with the backtick operator. This will invoke the command 'do_something_to' on every .c file anywhere in the directory tree headed by the current directory:

foreach f (`find . -name '*.c'`)
   do_something_to $f
end

The find command can of course do the above directly by using find's -exec option.

 

[quicknote]

, not a specific list of values

Yes, it is possible to do a for loop at the command line over all files in a given directory using the tcsh shell. The syntax for a for loop in tcsh is slightly different than in other shells, but it is still possible to achieve the desired result. Here is an example of how you could loop over all files in a directory and apply a sed command to each one:

foreach file (`ls *.txt`)
sed -i 's/old_text/new_text/g' $file
end

In this example, the "foreach" command is used to create a loop that iterates over each file in the directory that ends in ".txt". The "ls" command is used to list all the files that match the pattern, and the backticks (`) are used to capture the output of the command and store it in the "file" variable. Then, the "sed" command is used to perform the desired text replacement on each file, using the "file" variable as the input. The "-i" flag is used to perform the replacement in-place, meaning it will overwrite the original file.

It is important to note that the "foreach" command in tcsh does not have the same functionality as a traditional "for" loop, as it does not allow for a specific list of values to be iterated over. Instead, it iterates over a set of values that are generated by a command, as shown in the example above.

In conclusion, it is possible to use a for loop in tcsh to iterate over all files in a given directory and perform commands on each one, such as using sed to make text replacements. However, the syntax and functionality may differ slightly from other shells, so it is important to consult the tcsh documentation for more information.