在Linux中使用“ sed”命令替换文本

Question

I have a specific question related to the usage of sed in linux.

Suppose there is a String "Hello to the world version 1.0.0.1"

Now I want to take the new version from a file and update this

For example the new version is present in /etc/NewVersion

So can we do something like this :

$newVersion = "/etc/NewVersion"
sed -i "s/1.0.0.1/$newVersion/g" /etc/motd

Also is there a way that suppose the last number of the version changes, from 1.0.0.1 to something else like 1.0.0.2 , how can i make it generic that no matter what the version Im able to fetch the new version from the file path and update it with sed?

Answer 1

sed doesn't really support passing parameters very well. A better solution would be awk:

awk -v overs="1.0.0.1" -v newver="1.0.0.2" '$0 ~ overs { flag=0;match($0,overs);print substr($0,1,RSTART-1)newver } $0 !~ overs { flag=1 } flag' /etc/motd

Pattern match for the old version number. If it exists, stop the line printing by setting flag=0. Then match the old version number and print the rest of the line plus the new version number. Otherwise, set flag=1 and print the line.

Answer 2

With sed and a bash command substitution to read from /etc/NewVersion , and assuming that your New Version text will never contain a forward-slash:

sed -i "s/\(Hello to the world version \).*/\1"$(</etc/NewVersion)"/" /etc/motd

This replaces (with -i "in-place" editing of /etc/motd) the string "Hello to the world version ", followed by anything, with the "Hello" text (captured with the parenthesis and referred to by the \\1 , followed by the contents of /etc/NewVersion .

Or, if you want to allow any contents in /etc/NewVersion , use ed :

ed -s /etc/motd <<< $'1c\nHello to the world version '"$(</etc/NewVersion)"$'\n.\nwq'

This edits /etc/motd in script ( -s ) mode, passing it the quoted string as input (commands for ed):

1. on line 1 , c hange it to:
2. Hello to the world version followed by the contents of /etc/NewVersion
3. . stop input mode for the c command
4. w rite and q uit