#!/bin/bash
if grep "$1" "$3" > /dev/null; then
mv $3 $3.bak
sed "s/$1/$2/g" $3.bak > $3
fi
Hello there, I am trying to edit this code so that it will produce a shell script called "subst" that will apply a substitution to any number of files given on the command line.
For example, putting in
~/text/subst happy cow myFile1.txt myFile2.txt myFile3.txt
would substitute in all three files.
When I try to execute it says,
Checking subst...
/home/jzhang/UnixCourse/scriptAsst/subst is not executable.
Seeing this, I figured well, I do chmod +x subst, but that didn't work either because the file doesn't exist yet...not sure what to do now.
That seems rather the long way around. Why not just write a script that does that in the first place?
Think I remember giving you an example for one, too.
[edit] yes, I did.
if [ "$#" -lt 3 ]
then
echo "usage: a b file1 file2 ..."
exit
fi
A="$1"
shift
B="$1"
shift
while [ "$#" -gt 0 ]
do
echo "substitute $A for $B in $1"
shift
done
You complained you didn't know how to do a while loop yet, but it's easier than building rube-goldbergian script-generator generator.
How a while loop works is simple:
while [ condition ]
do
something
done
where [ condition ] is a statement exactly like you'd cram in an if. As soon as the statement becomes false, it stops repeating the code between do and done. My condition, [ "$#" -gt 0 ] , is true whenever there's one or more arguments left (a number that decreases by one every time you shift).
How shift works is also simple. Say you have $1=string, $2=replacement, $3=file1, $4=file2. After a shift, you have $1=replacement, $2=file1, $3=file2. So I just save string and replacement for later, get rid of the original $1 and $2, then loop through all the remaining filenames...
can be done using :
#!/bin/bash
array=( "${@}" )
if [ ${#array} -lt 3 ];then
echo "Usage: $0 a b file1 file2 ..."
else
for (( i=1 ; ++i<${#array}; ));do
grep ${array[0]} ${array} > /dev/null && sed -i.bak "s/${array[0]}/${array[1]}/g" ${array}
done
fi
Ok thanks for the reply! 
For Corona:
It's part of the book assignment so I have to do what it says, I don't have a choice haha. So unfortunately, your code doesn't work :(.
Danmero:
Code doesn't work unfortunately.
Here is what the book says:
Create a new script, subst2, taking the parameters: the string to be replacedthe string with which to replace itthe name of the file in which to make the substitution, that performs the substitution and backup file creation when the target string occurs somewhere in the file, but leaves the file completely unchanged (and does not create the .bak file) if the string being replaced is nowhere in the file.
Generalize your subst2 script, producing a new script subst that will apply a substitution to any number of files given on the command line. For example ~/UnixCourse/scriptAsst/subst foo bar myFile1.txt myFile2.txt myFile3.txt should apply the same substitution throughout each of the three files named there.
doesn't work is not very useful to solve your problem, try to post any/all errors returned by your script.
Take a look at the following script:
#!/bin/bash
array=( "${@}" )
if [ ${#array} -lt 3 ];then
echo "Usage: $0 a b file1 file2 ..."
else
for (( i=1 ; ++i<${#array}; ));do
grep ${array[0]} ${array} > /dev/null &&\
echo "ON FILE ${array} SUBSTITUTE ${array[0]} FOR ${array[1]} AND BACKUP FILE ${array} TO ${array}.bak" ||\
echo FILE ${array} UNCHANGED.
# grep ${array[0]} ${array} > /dev/null && sed -i.bak "s/${array[0]}/${array[1]}/g" ${array}
done
fi
Running this script give me the following output:
/temp/script happy cow myFile1.txt myFile2.txt myFile3.txt
ON FILE myFile1.txt SUBSTITUTE happy FOR cow AND BACKUP FILE myFile1.txt TO myFile1.txt.bak
FILE myFile2.txt UNCHANGED.
FILE myFile3.txt UNCHANGED.
Where only file myFile1.txt match the pattern.
---------- Post updated at 08:09 AM ---------- Previous update was at 08:04 AM ----------
Please read the Forum Rules regarding the homework's and assignments.
Throw out the book, get one where you're allowed to use loops in a sane way.
Unless this is homework, in which case you're in the wrong subforum. There's special rules for homework.
Oh, sorry, correction, I think there was alot of confusion about what I was looking for: I am just trying to edit this code:
#!/bin/bash if grep "$1" "$3" > /dev/null; then mv $3 $3.bak sed "s/$1/$2/g" $3.bak > $3 fi
So that it will take in any amount of files and make the substitution.
Corona, i was trying to use your code:
if [ "$#" -lt 3 ] then echo "usage: a b file1 file2 ..." exit fi A="$1" shift B="$1" shift while [ "$#" -gt 0 ] do echo "substitute $A for $B in $1" shift done
I used this code, and it outputted this when I did this: ~/test/subst happy dog happy.txt sad.txt neutral.txt
substitute happy for dog in happy.txt
substitute happy for dog in neutral.txt
substitute happy for dog in sad.txt
When I checked the file, nothing happened to the files.
That's because his code just echo's what it would do - you need to uncomment the code that actually does the sed.
Have a look above and see the red comment - remove that.