sed substitution with bash variables

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sed in bash script

Trying to change values in a text file using sed in a bash script with the line,

sed 's/draw($prev_number;n_)/draw($number;n_)/g' file.txt > tmp

This will be in a for loop. Not sure why it's not working. Any suggestions?

bash - How do I use variables in a sed command?, When you use single quotes for strings, its contents will be treated literally, so sed now tries to replace every occurrence of the literal $var1 by  Sed variable substitution when variable constructed of a directory path Hello, i have another sed question.. I'm trying to do variable substition with sed and i'm running into a problem. my var1 is a string constructed like this: filename1 filerev1 filepath1 my var2 is another string constructed like this: filename2 filerev2 filepath2 when i do

variables within single quotes are not expanded, within double quotes they are, use double quotes in this case.

sed "s/draw($prev_number;n_)/draw($number;n_)/g" file.txt > tmp

You could also make it work with eval, but dont do that!!

How can I use variables in the LHS and RHS of a sed substitution , So, bash then passes them to sed. Sed gives an error because $ can occur only at the end of line. Instead if we use double quotes, i.e., "s/$old_run/$new_run/" , then bash sees this and interprets $old_run as a variable name and makes a substitution (this phase is called variable expansion). How to edit a string within a variable. The shell is a rather good tool for manipulating strings. The Bash shell, in particular (which is the default on almost every Linux distribution, and available on almost every Unix, too), has some strong string manipulation utilities built-in.

sed "s/draw($prev_number;n_)/draw($number;n_)/g" 

would this work?

Environment variable substitution using Sed, sed -i -e "s/INSTHOME/$HOME/g" config.ini. s is used to replace the found expression INSTHOME with $HOME; g stands for "global", which  In our previous sed articles we learned — sed printing, sed deletion, sed substitute , sed file write, and sed multiple commands. In this article, let us review some interesting workarounds with the “s” substitute command in sed with several practical examples.

You can use variables like below. Like here, i wanted to replace hostname ie, system variable in file. I am looking for string look.me and replacing that whole line with look.me=<system_name>

sed -i "s/.*look.me.*/look.me=`hostname`/"

You can also store your system value in other variable and can use that variable for substitution.

host_var=`hostname`

sed -i "s/.*look.me.*/look.me=$host_var/"


Input file :

look.me=demonic

Output of file (assuming my system name is prod-cfm-frontend-1-usa-central-1 ) :

look.me=prod-cfm-frontend-1-usa-central-1

sed, Variables inside single quotes ' don't get expanded by POSIX compatible shells, so using a shell variable in a sed substitution requires the use of double quotes  The $ character is used for parameter expansion, arithmetic expansion and command substitution. You can use it for manipulating and expanding variables on demands without using external commands such as perl, python, sed or awk. This guide shows you how to use parameter expansion modifiers to transform Bash shell variables for your scripting needs.

Replace strings in files with sed, the bash command – clubmate.fi, Variables can be used just as well, only they need to be interpolated and the first sed  Bash variables and command substitution Using variables to refer to data, including the results of a command. An essential feature of programming is the ability to use a name or a label to refer to some other quantity: such as a value, or a command. This is commonly referred to as variables.

How To Use Bash Parameter Substitution Like A Pro, such as perl, python, sed or awk. This guide shows you how to use parameter expansion modifiers to transform Bash shell variables for your  Variables inside ' don't get substituted in bash. To get string substitution (or interpolation, if you're familiar with perl) you would need to change it to use double quotes " instead of the single quotes:

sed substitution and shell variables, Am trying to substitute the value of a shell variable with the value of another shell variable. [bash] command line substitution with environmental variables. 1. Basic text substitution using ‘sed’ Any particular part of a text can be searched and replaced by using searching and replacing pattern by using `sed` command. In the following example, ‘s’ indicates the search and replace task.

Comments
  • Maybe also mention that if the variable contains slashes, you need to use a different delimiter which doesn't occur in the string (or backslash-escape every occurrence of the delimiter). The slash is a common default for s but you can use any punctuation character; sed "s%draw($prev_number;n_)%draw($number;n_)%g" file.txt or s#from#to#g or s_from_to_g etc.
  • it doesn't work if the variable contains new-lines ("\n")
  • but it did once escaped (for my use cases) also slashes: changelogEscaped=$(sed -e 's%\/%\\/%g; $!a\'$'\n''\\n' <<<"$changelog" | tr -d '\n') Thanks for the link above.
  • Thanks that worked. Would you mind explaining what you mean by expanded? My intuition tells me that it should be something like, variable substituted. Also why not use eval?