[Date Prev][Date Next] [Thread Prev][Thread Next] [Date Index] [Thread Index]

Re: Read/Write files from a script?

The $(<fileName) construct is very nice, if you're using a shell that supports it. But ash (at least the version I have) doesn't, so what to do if you want/need to be portable across all Bourne type shells? There is a feature that will work in all the Bourne shells that I'm familiar with, using I/O redirection and 'exec': 

exec 5<fileName # for reading; to write file do: exec 5>fileName
while read inputLine
do
  something_on $inputLine
done <&5
And, if you need multiple files open for reading and/or writing, combine on one line with a single 'exec': 

exec 4<existingFile 5>newFile 6>>existingAppend
And so on. The general form to use the file descriptor created in the exec command line is 'redir-op&#', where # is the desired file descriptor and redir-op is one of '<' or '>'. Note that when you use the append form to create the descriptor (as with 6, above) you do *not* use the append operator when using it. '>&6' will append if 6 was created in append mode and overwrite if not. 

Bob

LeVA wrote:

2006. július 19. 16:31,
Mladen Adamovic <adamm@blic.net>
-> Debian User <debian-user@lists.debian.org>,:


Tony Terlecki wrote:


Is there a shell command to read files?  I want to open a text file,
loop through each line and parse the line of text.


Depending on what you want to do:

man sed
man awk


Yeah, but he asked about shell commands which read files, and that is 'cat'
so my addon to your answer is : see also 'man cat'
"The purpose of cat is to concatenate (or "catenate") files. If it's only one file, concatenating it with nothing at all is a waste of time, and costs you a process." — Randal L. Schwartz 


In bash script you might  use something like
for i in $(cat yourfile);
do
       do_something_with $i
done




http://sial.org/howto/shell/useless-cat/

In a bash script you should use something like this:

for i in $(<yourfile)
do
        do_something_with $i
done


Daniel
Reply to: