CODEWITHSUNDEEP
bashsedtext-processing
vincent pham
vincent pham

Reputation: 129

appending new line with sed command in bash

Hi I have trouble appending newline by sed command. I was instructed to write a command that update host file. Also, My sed command is written in bash script, though it kept outputting error message. It said "sed: -e expression #1, char 93: extra character after command."

this is the contend I want to add to my hosts file.

# Gateway
10.0.0.1    schoolhost  it20
# Addresses for the Windows
10.0.0.240  host1 it21
10.0.0.241  host2 it22

This is the command I wrote in bash script.

sed -i "/hosts/a \
\n# Gateway \
\n10.0.0.1    schoolhost  it20 \
\n# Addresses for the Windows PCs \
\n10.0.0.240  host1 it21 \
\n10.0.0.241  host2 it22" hosts

Upvotes: 1

Views: 606

Answers (2)

dawg
dawg

Reputation: 103834

Given:

$ cat file
line 1
line 2
line 3

And:

$ echo "$add_this"
# Gateway
10.0.0.1    schoolhost  it20
# Addresses for the Windows
10.0.0.240  host1 it21
10.0.0.241  host2 it22

You can do several things to add those text elements together.

The first is to use cat (recalling the name comes from concattenate):

$ cat file <(echo "$add_this")
line 1
line 2
line 3
# Gateway
10.0.0.1    schoolhost  it20
# Addresses for the Windows
10.0.0.240  host1 it21
10.0.0.241  host2 it22

Or, you can use awk the same way:

$ awk '1' file <(echo "$add_this")
# same output

Or, an empty sed:

$ sed -e '' file <(echo "$add_this") 
# same output

Or with printf:

$ printf "%s%s\n" "$(cat file)" "$add_this"
# same output

Bottom line is you are only adding two pieces of text together and there are many ways in Unix to do that.

Then redirect the output of any of those (likely cat) to a temp file then move the temp file onto the source file:

$ cat file <(echo "$add_this") >/tmp/tmp_file && mv /tmp/tmp_file file
$ cat file
line 1
line 2
line 3
# Gateway
10.0.0.1    schoolhost  it20
# Addresses for the Windows
10.0.0.240  host1 it21
10.0.0.241  host2 it22

Upvotes: 0

chepner
chepner

Reputation: 531165

I don't see a need for sed here. Just use cat and a here document.

cat <<EOF >> hosts
# Gateway
10.0.0.1    schoolhost  it20
# Addresses for the Windows
10.0.0.240  host1 it21
10.0.0.241  host2 it22
EOF

Upvotes: 1

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