Hi
please help me with the script of going into a directory and edit each file in there. e.g. in /temp there are 8 files and each contain content that contains ABC as consecutive characters somewhere. so, the challenge is to change the ABC to TTT each time it occurs in all the 8 files. the following is what i attampted:

cd /home/temp
for file in temp_files
do
file2=`cat $file | tr "ABC" "TTT"`
done


This seems not to work.
Please assist!

What does not work exactly? Do you receive some error or just don't get the expected result? Two things I can notice, here. First, the script does not actually edit the files: it simply stores the file content in a shell variable, which is overwritten at each loop. Second, the tr command is not suitable for this kind of substitution, since "ABC" is not interpreted as a string of three characters but as a set of characters, in the sense that every occurrence of A or B or C is substituted by the characters in the second set, not only the literal ABC string.

I suggest to look at the sed editor which gives the possibility to substitute a whole pattern and to edit the files in place, using the -i option. This is a very good tutorial on sed. Anyway, give it a try and ask again if you encounter any problem.

'tr "ABC" "TTT" < input-file > different-output-file && mv different-output-file input-file' translates all occurrences of "A" to "T", all occurrences of "B" to "T", and all occurrences of "C" to "T".
'tr "ABC" "CBA" < input-file > different-output-file && mv different-output-file input-file' translates all occurrences of "A" to "C", all occurrences of "B" to "B", and all occurrences of "C" to "A".

'sed -i "s/ABC/TTT/g" input-file' will change all occurrences of "ABC" to "TTT" in input-file.

A for loop will operate on all your files in turn:

for file in temp_files; do
sed -i 's/ABC/TTT/g' $file
done

Why the loop?


sed -i 's/ABC/TTT/g' /temp_folder/*

I'd prefer to not give complete solutions to homework questions, just give some hints and let the student move his brain. Maybe it was not so clear it is homework, anyway.

Good point... I tend to use them when I know I'll be doing more with a file than a single operation like that, which more often than not, I will be. Habit, I guess.

And if it is, he has only himself to blame if he has no clue later how to cope with editing large numbers of files. Oh, well.

Thanks guys! You guys are great! All the tips worked perfectly fine although I struggled because I confused ' with ` and it gave me errors but I managed to come around it.

And a big thanks to colucix for the tutorial, it will keep me reading:-)
And for all of you guys I dont mean you give me tutorials as solutions please, but they can always make a good company with the solutions I believe :-).