How to find and replace string in my .txt files?

Question

I have files in which I am storing some credentials, I want shell script to read that file and check if current cred matches searched string, replace that at that location only.

I tried below code but it always append and does not even replace string.

cat $FILESOURCE | sed -e "s/$TEXTTOSEARCH/$TEXTTOREPLACE/g" >> $FILESOURCE

where

• FILESOURCE = my .txt file to read
• TEXTTOSEARCH = string to search
• TEXTTOREPLACE = text to replace

Note: I don't want to mess up existing file, instead it just open file for reading check if searched string found, then replace it, if not found dont do anything to file.

Answer 1

Of course it appends, since you are using >>, which means append.

What do you have in $TEXTTOSEARCH? Are there letters only or any special characters? If you have special characters that have special meaning in regular expression, you have to escape them in order to work correctly. For instance . means any character. You should replace it with \. in your $TEXTTOSEARCH. Look here for more details.

There are many ways how to handle your files. I would suggest you use

sed -i.bak -e "s/$TEXTTOSEARCH/$TEXTTOREPLACE/g" $FILESOURCE

In that way sed will replace text in your file and make a backup with .bak extension. If you want it another way specify more in detail. Your question is not very clear, as you say you do not want to mess up existing file, and you want to replace text in that file?