sed script append to lines starting with?

Question

I'm trying to write a basic sed script, I want to append to lines that start with SSID:. Here is what I'm trying now:

#!/bin/sed -f

/^SSID:/ s/*/},\n{/

With the following input:

SSID:                                   '2KLIC Guests'
BSSID:                                  F0:9F:C2:21:03:BA
MODE:                                   Infrastructure
FREQ:                                   2437 MHz
RATE:                                   16 MB/s
SIGNAL:                                 100
SECURITY:                               WPA2
ACTIVE:                                 yes
SSID:                                   'CBMS-2.4GHz'
BSSID:                                  10:BE:F5:25:FD:60
MODE:                                   Infrastructure
FREQ:                                   2412 MHz
RATE:                                   16 MB/s
SIGNAL:                                 0
SECURITY:                               WPA WPA2
ACTIVE:                                 no
SSID:                                   'CIK1000M_AC2.4G_3714'
BSSID:                                  D0:60:8C:03:DB:B4
MODE:                                   Infrastructure
FREQ:                                   2422 MHz
RATE:                                   16 MB/s
SIGNAL:                                 0
SECURITY:                               WPA2
ACTIVE:                                 no

I also tried escaping the :. Can someone explain what I'm doing wrong here?

Answer 1

To just substitute the whole line,

s/^SSID:.*/},\n{/

If you wanted to keep some or all of the SSID line's contents, then try capturing in the initial regex.

s/^\(SSID:.*\)/\1\n},\n{/

Answer 2

Your sed expression:

/^SSID:/ s/*/},\n{/

This is almost correct, but * will match a literal * (since it's the first character in the regular expression).

Using your way of addressing the line that you'd like to modify:

/^SSID:/s/^/},\n{/

This would find any line beginning with the string SSID: and would substitute in },\n{ at the start of those lines.

Note that this requires GNU sed to interpret the escape sequence \n as a newline in the replacement text.

With non-GNU sed, you would write

/^SSID:/s/^/},\
{/

or, if you did this from the command line with a shell like bash that understands $'...' as a "C string":

sed '$/^SSID:/s/^/},\\\n{/'

(the \\\n is for an escaped \ followed by \n)