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help with a ksh script

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# 1  
Old 05-03-2007
help with a ksh script
I am trying to substitute words within multiple files...I posted the first script (https://www.unix.com/showthread.php?t=37505) in tcsh and still for some reason getting nowhere so I tried it in ksh.

Code:
#!/bin/ksh
pattern1=$1
pattern2=$2

if [[ $# != 2 ]]
then
print "Usage: $0 $pattern1 $pattern2"
exit
fi


for file in $(ls)
do
sed "s/$pattern1/$pattern2/g" $file > $file
done

The problem is that when I run the script, it seems it gets to here
Code:
if [[ $# != 2 ]]
then
print "Usage: $0 $pattern1 $pattern2"
exit
fi

and never makes it to
Code:
for file in $(ls)
do
sed "s/$pattern1/$pattern2/g" $file > $file
done

because I don't see any changes made to the .txt files when I do
Code:
more test1.txt

cause I still see the old word there.
# 2  
Old 05-03-2007
you have to use a temp file

sed "s/$pattern1/$pattern2/g" $file > /tmp/file
mv /tmp/file $file

or something like that
# 3  
Old 05-03-2007
Quote:
Originally Posted by csnewbie84
I am trying to substitute words within multiple files...I posted the first script (https://www.unix.com/showthread.php?t=37505) in tcsh and still for some reason getting nowhere so I tried it in ksh.
...
The problem is that when I run the script, it seems it gets to here
Code:
if [[ $# != 2 ]]


Use -ne for numeric comparisons, and don't use the non-standard [[...]]:
Code:
if [ $# -ne 2 ]

Quote:
Code:
then
print "Usage: $0 $pattern1 $pattern2"
exit
fi

and never makes it to
Code:
for file in $(ls)


Not only is ls unnecessary, but it will break your script if any filenames contain spaces or other pathological characters. Use:

Code:
for file in *

Quote:
Code:
do
sed "s/$pattern1/$pattern2/g" $file > $file
done

because I don't see any changes made to the .txt files when I do
Code:
more test1.txt

cause I still see the old word there.

You're lucky to see anything at all. Normally, the shell truncates the file before the command is even started.

The standard method is to save the output to a temporary file, then move or copy it over the original file if the command succeeded:

Code:
sed -e '...' FILE > tempfile && mv tempfile FILE

Or copy it first and send the output to the original file:

Code:
cp FILE tempfile
sed -e '...' tempfile > FILE

Some version of sed have an option, -i, that edits the file in situ.

A trick that allows redirection to the same file is:

Code:
{ rm FILE; sed -e '...' > FILE; } < FILE

# 4  
Old 05-03-2007
Quote:
Originally Posted by cfajohnson

Use -ne for numeric comparisons, and don't use the non-standard [[...]]:
Code:
if [ $# -ne 2 ]


Not only is ls unnecessary, but it will break your script if any filenames contain spaces or other pathological characters. Use:

Code:
for file in *


You're lucky to see anything at all. Normally, the shell truncates the file before the command is even started.

The standard method is to save the output to a temporary file, then move or copy it over the original file if the command succeeded:

Code:
sed -e '...' FILE > tempfile && mv tempfile FILE

Or copy it first and send the output to the original file:

Code:
cp FILE tempfile
sed -e '...' tempfile > FILE

Some version of sed have an option, -i, that edits the file in situ.

A trick that allows redirection to the same file is:

Code:
{ rm FILE; sed -e '...' > FILE; } < FILE

SO I don't have to use "$" for FILE right?
# 5  
Old 05-03-2007
Quote:
SO I don't have to use "$" for FILE right?

If it's a variable, of course you do.

In the example, it is just a generic filename. You replace it with the name of your file. If you use a variable, quote it.

Last edited by cfajohnson; 05-03-2007 at 06:47 PM..
# 6  
Old 05-03-2007
Quote:
Originally Posted by cfajohnson
[INDENT]
If it's a variable, of course you do.

In the example, it is just a generic filename. You replace it with the name of your file. If you use a variable, quote it.
Thanks again! I will try that and let you know what happens.
# 7  
Old 05-03-2007
cfajohnson or anyone else,

personal opinion...would you use this in the script

Code:
if [[ $# != 2 ]]
then
print "Usage: $0 $pattern1 $pattern2"
exit
fi

cause I think it don't have to be there...I would thought the the do statement is the important part of the script.
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