SED 语句替换 Shell 脚本中的变量

Question

I've created a bash script that gets an IP Address as variable ${MYSQL_SERVER_IP} . I then want to pass it in a sed to replace the previous IP address in a settings.py file. Here is the closest I have gotten to a sed statement that actually runs without error:

export MYSQL_SERVER_IP= '172.19.0.2'
sed -i -e '/DB_HOST =/c\DB_HOST = os.getenv( '\''IP'\'', '\''${MYSQL_SERVER_IP}'\'')\' Flask-URL-Shortener/settings.py

The problem is that the script doesn't replace the variable with the value of the variable.

In the file before running the script:

DB_HOST = os.getenv( 'IP', '172.31.0.2')

Currently the output I get is wrong:

DB_HOST = os.getenv( 'IP', '${MYSQL_SERVER_IP}')

as I would like to obtain the following output:

DB_HOST = os.getenv( 'IP', '172.19.0.2')

This sed statement is the last line of code I need to fix to make my program work the way I want it to.

Answer 1

I don't think you want to be using c here. Just do:

sed -e '/DB_HOST\s*=/s/${MYSQL_SERVER_IP}/'"${MYSQL_SERVER_IP}"/

You can limit the replacement to the line containig DB_HOST = , but you don't need to try to do anything with that text in the replacement. Only replace the part that needs to be changed. Note that this will fail if MYSQL_SERVER_IP contains forward slashes, so you'll want to validate the data.

Answer 2

Based on your comment, it seems like you need the following command

sed '/DB_HOST/s/[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}/'"$MYSQL_SERVER_IP"'/' yourfile

where the substitution command s is applied only to the lines matching the DB_HOST pattern (you can make it more complicated, eg /DB_HOST *= */ , to match DB_HOST followed by = , the latter preceded and followed by zero or more spaces); the regexp of the s command contains 4 expressions matching between 1 and 3 digits ( [0-9]\\{1,3\\} ), interspersed with literal dots \\. .

Original answer

Please, if the next three lines do not describe your case, leave a comment and clarify.

Let's say myShortFile contains only this line (since it is a simple text file, all characters, $ included, are literal):

IP = $MYIP

Then, if you run such a bash script:

#!/bin/bash
MYIP="172.19.0.2"
sed 's/$MYIP/'"$MYIP"'/' myShortFile

you will get

IP = 172.19.0.2

The reason is that in the string concatenation '…'"…"'…' , the first and the third parts ( 's/$MYIP/' and / ) are interpreted literally by bash , since they are enclosed in single quotes ( ' ), whereas the $MYSIP in the middle piece "$MYIP" is expanded, since it is in between double quotes ( " ). The result is that bash will execute the command

sed 's/$MYIP/172.19.0.2/' myShortFile

which substitutes $MYIP in myShortFile with 172.19.0.2 and prints the resulting output to screen.