sed如何在第一行的末尾添加带有竖线的变量

Question

i want to append variable with string to the first line of my_file

sed -i "1 s/$/ $my_variable/" ~/my_file

Now i have this:

42 192.168.1.1 string_from_my_variable

It works. But the task become harder, now i need to add delimiter before string_from_my_variable

I tried to sed -i "1 s#$# \\|\\$my_variable#" ~/my_file , of course it does not help. I need to have this:

42 192.168.1.1 | string_from_my_variable

How can i do this ? Thanks for your attention.

Answer 1

Since you want to deal with literal strings that come from a shell variable, I would go with awk:

awk -v extra="$my_variable" 'NR == 1 { $0 = $0 "   |" extra } 1' file

Add the extra string to the first line and 1 at the end is the shortest way to write 1 { print $0 } , so every line gets printed.

To overwrite your original file:

# GNU Awk
awk -i inplace -v extra="$my_variable" 'NR == 1 { $0 = $0 "   |" extra } 1' file
# any Awk
awk -v extra="$my_variable" 'NR == 1 { $0 = $0 "   |" extra } 1' file > tmp && mv tmp file

Answer 2

我已经发现：

sed -i "1 s/$/ \\|$my_variable/" ~/my_file

Answer 3

I think there's a coincidence in your command sed -i "1 s#$# \\|\\$my_variable#" , the $# is a special parameter in the double quotation marks( "" ), which means the number of parameters are given , you can get more informations by man bash :

Special Parameters # Expands to the number of positional parameters in decimal.

so, your command is illegal.

# $# is a special parameter, so the command is illegal:
$ sed "1s#$#   |${my_variable}#" my_file 
sed: -e expression #1, char 32: unterminated `s' command
# when used ', the special meaning of $# is gone,
# and the command is legal, but doesn't work for your expection:
$ sed '1s#$#   |${my_variable}#' my_file 
42 192.168.1.1   |${my_variable}
# add a space beteween `$#`, and the command is legal too,
# but still doesn't work for your expection:
$ sed "1s#$ #   |${my_variable}#" my_file 
42 192.168.1.1

you can use a different delimiter instead of # :

my_variable="string_from_my_variable"
sed -i "1s/$/   |${my_variable}/" ~/my_file

PS:

1. the \\ before $my_variable should NOT exist.
2. the \\ before | is unnecessary if the delimiter is NOT | .