sed -e 's|PATH="\(.*\)"|PATH="/opt/man/common/bin:\1"|g' -i /etc/environment 行是什么意思

Question

以下命令是什么意思？

sed -e 's|PATH="\(.*\)"|PATH="/opt/man/common/bin:\1"|g' -i /etc/environment

Answer 1

It substitutes all the instances of

PATH="somestring"

with

PATH="/opt/man/common/bin:somestring"

in the file /etc/environment

In detail

• s|string1|string2| substitutes string1 with string2
  • the delimiter (in this case | ) is defined by the character following the substitute command ( s ). More common is / .
  • the flag g at the end tells sed to substitute all non-overlapping matches (and not only the first one)
  • the \( and \) define a group (in this case everything between the quotes)
  • the \1 is a back-reference to the first group
• -i is telling sed to apply the changes directly in the file (inline) instead of writing to standard output.

Edit

As pointed out in the comments this regular expression is very fragile.

• It will match the string anywhere (not only after a blank or the beginning of a line). It will for example match CDPATH="string"
• It will not match strings delimited by ' . It will not match PATH='somepath' .
• It will match strings in comments. For example # some comment with PATH="" in the text
• It will match inside other strings, for example STRING='PATH="somepath"