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My assignment asks that:

Create a directory ~/UnixCourse/scriptAsst. Turn the two-line version, above, of the substitution commands into a shell script, subst1 taking three parameters: the string to be replaced the string with which to replace it the name of the file in which to make the substitution.

For example,

`~/UnixCourse/scriptAsst/subst1 foo bar myFile.txt`

should replace all occurrences of foo in the file myFile.txt by bar, leaving the original file as myFile.txt.bak.

Similarly,

`~/UnixCourse/scriptAsst/subst1 abc "" aardvark.dat`

should remove (replace by the empty string) all occurrences of abc in the file aardvark.dat with nothing, leaving the original file as aardvark.dat.bak.

My code that I came up with is: 

#!/bin/bash set p1 = "$1" shift set p2 = "$1" shift set p3 = "$*" echo $p1 echo $p2 echo $p3 if grep "$p1" "$p3" > /dev/null; then mv "$p3" "$p3.bak" sed "s/$p1/$p2/g" "$p3.bak" > "$p3" fi

When I try to run:

./subst1 foo bar myFile.txt

I keep getting:

grep: : No such file or directory

Please help!! What am I doing wrong??

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  • 1
    What does the script print for the echo $p1...? Commented Dec 3, 2011 at 16:59
  • 2
    Did you copy and paste that exactly? The error looks like you have a stray : after your grep command. Commented Dec 3, 2011 at 17:07
  • That paste is exactly what I have Commented Dec 3, 2011 at 17:16
  • NVM, it's grep not being able to find a file with no name (""). Apparently $p3 isn't getting the filename. Commented Dec 3, 2011 at 17:31

3 Answers 3

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1

This is how you set variables:

p1="$1" shift p2="$1" shift p3="$1"

or in this case simply:

p1="$1"; p2="$2"; p3="$3"

Note:

  • try to use meaningful variable names, or simply use $1 directly.
  • there is grep -q so you don't have to redirect standard output.
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ok, this code helped. Now I get the error: subst1: Could not find the backup file (test 3). It's something for class, once I get this, Ill flow with everything else.
1

You don't actually need to do anything.

sed -i.bak "s/$1/$2/g" "$3"
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or use the parameters directly...

#!/bin/bash echo $1 echo $2 echo $3 if grep "$1" "$3" > /dev/null; then mv "$3" "$3.bak" sed "s/$1/$2/g" "$3.bak" > "$3" fi
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ok, this code helped. Now I get the error: subst1: Could not find the backup file (test 3). It's something for class, once I get this, Ill flow with everything else.
that code worked for me... what's the name and content of your input files?
im entering: ./subst1 foo bar myFile.txt for my tests
strange, I use the exact same command. And your myFile.txt exists in the same directory and contains some text (preferably some "foo"s :))?
ok, I see it now. I have to find out why the test isn't working. Because the .bak file is in the same directory for me too

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