Programming Forums > Script Programming > Bash / Shell Scripting

bryanlharris · Jun 18th, 2005, 12:37 PM

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:

(Toggle Plain Text)

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):

(Toggle Plain Text)

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):

(Toggle Plain Text)

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, 12:51 PM

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, 12:52 PM

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:

(Toggle Plain Text)

 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, 10:26 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:

(Toggle Plain Text)

#! /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, 10:40 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.

(Toggle Plain Text)

#!/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`....

(Toggle Plain Text)

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, 11:53 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, 12:31 PM

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, 10:10 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.

Jun 18th, 2005, 12:37 PM	#1
bryanlharris Newbie Join Date: Jun 2005 Location: Texas Posts: 3 Rep Power: 0	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: (Toggle Plain Text) Now is the time for all good men to come to the aid of their country. 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): (Toggle Plain Text) 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. 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): (Toggle Plain Text) 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. 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

Jun 18th, 2005, 12:52 PM	#3
Dameon Troll Join Date: Apr 2005 Location: Texas Posts: 732 Rep Power: 4	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: (Toggle Plain Text) for i in $(cat cat_file_1); do echo -n $i; echo -n ' '; done; echo 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. __________________ MD5(sig) = bcef75433db02e9ad9bf81d6f7c5c270 Last edited by Dameon; Jun 18th, 2005 at 12:58 PM.

Jun 20th, 2005, 10:26 AM	#4
jim mcnamara Hobbyist Programmer Join Date: Jun 2005 Location: New Mexico Posts: 228 Rep Power: 4	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: (Toggle Plain Text) #! /bin/ksh while read record do echo "$record" done < filename IFS="\n" for i in `cat filename` do echo "$i" done IFS=" " #! /bin/ksh while read record do echo "$record" done < filename IFS="\n" for i in `cat filename` do echo "$i" done IFS=" "

Jun 27th, 2005, 10:40 AM	#5
bryanlharris Newbie Join Date: Jun 2005 Location: Texas Posts: 3 Rep Power: 0	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. (Toggle Plain Text) #!/bin/bash while read record do echo "$record" done < file IFS="\n" for i in `cat file` do echo "$i" done IFS=" " #!/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`.... (Toggle Plain Text) 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 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

Jun 27th, 2005, 11:53 AM	#6
ballsaq Newbie Join Date: Mar 2005 Location: Australia Posts: 5 Rep Power: 0	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? __________________ War isn't won by the side with the most brains, rather it is lost by the side with the most dopes. :rolleyes:

Jun 18th, 2005, 12:51 PM	#2
bryanlharris Newbie Join Date: Jun 2005 Location: Texas Posts: 3 Rep Power: 0	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.

Jul 3rd, 2005, 10:10 AM	#8
mackenga Professional Programmer Join Date: Mar 2005 Location: Glasgow, Scotland Posts: 335 Rep Power: 4	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.

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Programming Forums > Script Programming > Bash / Shell Scripting

for, cat, and echo