Programming Forums - for, cat, and echo

Programming Forums (http://www.programmingforums.org/forumindex.php)

- Bash / Shell Scripting (http://www.programmingforums.org/forum26.html)

- - for, cat, and echo (http://www.programmingforums.org/showthread.php?t=4498)

bryanlharris

Jun 18th, 2005 11:37 AM

for, cat, and echo

This is something I am curious about. I tried these commands and
expected one behavior but received another. Can anyone explain
further?

Conditions:
I have a file on my computer with the following contents:

Now is the time

for all good men

to come to the aid

of their country.

Expected Behavior(this doesn't really happen, but I wish it did):

for i in `cat file_1`; do echo $i; done





Now is the time

for all good men

to come to the aid

of their country.

Actual Behavior(this is what really happens):

for i in `cat file_1'; do echo $i; done





Now

is

the

time

for

all

good

men

to

come

to

the

aid

of

their

country.

I just don't understand why it is putting each word on a different line. Can anyone acheive the expected behavior? What am I doing wrong?

-Bryan

bryanlharris

Jun 18th, 2005 11:51 AM

By the way I posted this same thing on alt.comp.lang.shell.unix.bourne-bash about four days ago and no replies. I guess that place is dead.

Dameon

Jun 18th, 2005 11:52 AM

Echo by default outputs a newline character at the end of what you input. According to the man page, you can use the -n option to prevent this. Try changing your second statement to "do echo -n $i;". Note however that spaces are removed when doing a for, so you will have to re-add them.

My solution which is likely against every bash coding guideline in existance:

for i in $(cat cat_file_1); do echo -n $i; echo -n ' '; done; echo

The last echo is to add a newline to the end.

jim mcnamara

Jun 20th, 2005 9:26 AM

for loops are not used to read whole lines of text input, normally. This is because you get wierdness with IFS when you try to set it to newline.

The reason is that for reads fileds as separated by a space rather than a whole record
like the read command does. Try playing with IFS

try this:

#! /bin/ksh

while read record

do

    echo "$record"

done < filename



IFS="\n"



for i in `cat filename`

do

    echo "$i"

done

IFS=" "

bryanlharris

Jun 27th, 2005 9:40 AM

Thanks jim mcnamara for the great response. I think I will start using that read statement from now on. When running the for loop with IFS="\n" I do in fact get really strange results.

#!/bin/bash



while read record

do

echo "$record"

done < file



IFS="\n"



for i in `cat file`

do

echo "$i"

done

IFS=" "

My results look really nice using read and really weird using for i in `echo file`....

now is the time for

all good men to come

to the aid of their

countrymen.



ow is the time for

all good me

 to come

to the aid of their

cou

tryme

ballsaq

Jun 27th, 2005 10:53 AM

I might be wrong, but wouldn't you want IFS="\\n" because your looking for \n as the line terminator. And for it to read that it needs the extra \ or am I just losing my mind here?

TooDice

Jun 27th, 2005 11:31 AM

Quote:

Originally Posted by ballsaq

I might be wrong, but wouldn't you want IFS="\\n" because your looking for \n as the line terminator. And for it to read that it needs the extra \ or am I just losing my mind here?

I know what you're getting at but I think you're thinking a little too hard about it. IFS=\\n would actually look for the string "\n" as you're escaping the \ character. You shouldn't be looking for that string, you need to look for a new line character. Therefore "\n" is correct. It's difficult to explain, did anyone understand that?

mackenga

Jul 3rd, 2005 9:10 AM

Wouldn't there be an extra round of substitution anyway? This would mean using \\n was equivalent to \n, so you'd still be as well to save a byte, but I think you'd end up with a newline as the field separator either way. Keeping track of quoting and substitution is the main reason you'll rarely see me outside of tclsh. I'm too stupid for bash.

All times are GMT -5. The time now is 4:31 PM.