How to use variables with SED in Bash?

How to use variables with SED in Bash?

In order for our variables to be recognized and interpreted we need to use ” “, double quotes around our command. And to avoid some (not all) issues with strings possibly being passed in without escaping we can change our delimiter from / to |. Updates to our command and portability have drastically improved with this small change.

Why is SED giving me an error about an unterminated ` s’?

Awk has a notion of variable, and a command line syntax to set the initial value of a variable. In this case $VAR contains a character which is interpreted by sed as the trailing slash. As others have mentioned here, it depends on the content of your FOO* variables.

Are there any examples of SED in Linux?

In a command line environment, you will find there is more than one solution to a given task. However, for the most part, you want to go with the path that yields the least resistance. Here is a list of examples sed commands with corresponding equivalent commands, where some will be covered in detail below. 1.

Can You interpolate a variable in a sed command?

You cannot safely interpolate a variable in a sed command, because the substitution is performed by the shell, not by sed. The value of the variable becomes sed syntax. For example, in “s/TMPFOO1/$FOO1/”, if $FOO1 contains a newline, this will cause a syntax error like the one you observed.

How to find and replace string values with SED?

If you’ve every wanted to do some simple find and replace on string values sed is pretty straightforward way to do it from the command line or a script. Our starting sed command: In this command we define a few things:

What happens if there is no match in SED?

If no match is found, the variable will be set as i=0. sed (Stream EDitor) is not the right tool for this kind of things: you can simply use a bash if statement to match your input against a regex:

When to use quote in a sed command?

When you require the quote character in the replacement string, you have to precede it with a backslash which will be interpreted by the shell. In the following example, the string quote me will be replaced by “quote me” (the character & is interpreted by sed):

When to use single quotes or double quotes in SED?

It’s very simple when the command is enclosed in single quotes: what you see is exactly what sed sees. When using double quotes, however, your string is going to be interpreted by the shell before being passed on to sed, and you must take into account any modifications, some of which might not be what you want.

What’s the difference between single quotes and double quotes in Bash?

This is actually related to bash, rather than just the sed command. Double quotes evaluate the expression inside, whereas single quotes preserve the literal value of each character. More info here: https://stackoverflow.com/questions/6697753/difference-between-single-and-double-quotes-in-bash.

Why does SED not work in a shell script?

The sed command works as expected at the command prompt, but does not work in a shell script. Why is that, and how can I fix it? Use double quotes for the sed expression.

How to replace a string with quote in SED?

When you require the quote character in the replacement string, you have to precede it with a backslash which will be interpreted by the shell. In the following example, the string quote me will be replaced by “quote me” (the character & is interpreted by sed): sed -i “s/quote me/\\”&\\”/” “$file”.

Is it possible to substitute a variable in Bash?

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:

Is there a way to do somthing in SED?

You can do that by escaping all the problematic characters in the variable, so that sed takes them literally. And, this escaping can be done using sed as well. If you’re using BREs (Basic Regular Expressions) (the default in sed), you can do somthing like this:

How to replace a pattern in Bash using SED?

$ {parameter/pattern/string} — replace the first match of pattern with string. $ {parameter//pattern/string} — replace all matches of pattern with string. website=$ {website // / / \\\\/} ^ ^ ^ ^ | | | | | | | string, ‘\\’ needs to be backslashed | | delimiter | pattern replace globally

How to pass arbitrary text to SED Unix?

Alternatively, you can do it in one go by playing with IFS and using the read builtin: SiegeX’s answer is better for this particular case, but you should also know how to pass arbitrary text to sed. sed is expecting filenames as its second, third, etc. parameters, and if it doesn’t find any filenames, it reads from its standard input.