Need some help with sed/regexp and bash scripting

[AncientPC]

If this would be better done with perl let me know.

What I want to do is output the current time, last minute load, and battery usage into a file (and then run every minute as a cron job).

What I have thus far is:

#!/bin/bash

#format: #time,battery %,load

tmp=~/battery.tmp
output=/var/log/battery.log

date %H:%M, > $tmp
acpi -b | sed -e 's/.*: //g' -e 's/[[:space:]]//g' >> $tmp
cat $tmp | sed -e 'N' -e 's/\n//g' >> $output
rm -f $tmp

exit

I have a few questions.

1) How do I extract information using sed as opposed to removing all unnecessary information? I guess what I'm looking for is a function that returns a substring based off regexp.

For example I would something that did this:

acpi -b | <some command> [...%] | sed -e 's/[[:space:]]//g'
77%

2) I'm currently retrieving last minute's load by using

w | sed -e 's/.*, //g'
0.67
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
ting :0 - 17:38 ?xdm? 2:49m 0.27s x-session-manag
ting pts/0 :0.0 17:38 33:13m 5.27s 5.04s top
ting pts/1 :0.0 17:39 31:42m 0.14s 0.14s bash
ting pts/2 :0.0 17:40 3:38m 0.35s 0.35s bash
ting pts/3 :0.0 17:56 1.00s 0.21s 0.01s w
ting pts/4 :0.0 18:08 60.00s 0.16s 0.16s bash

How do I get rid of the other lines?

3) As you've noticed above I'm deleting pattern spaces using s/<regexp>//g'. I still don't understand how to use sed -e /<regexp>/d correctly.

4) I read somewhere that you could store the stdout contents of a command in bash scripting by simply assigning a variable but it doesn't seem to work for me.

#/bin/bash

a='ls -al'
echo $a

exit

Running the above lines gives me:

./test.sh
ls -al

[Ramses de Norre]

1) Use sed's p command to print text, I don't really understand what you want to achieve so I can't help you better, give a detailed example if you still don't understand (I don't have acpi so I don't know what it outputs).

2) Use head, I'd do it like this: w|head -1|cut -f13 -d" ", It's a bit more difficult with sed...

3) What is it you don't understand? sed -e 's/<regex>//g' does the same as sed -e '/<regex>/d'.

4) Instead of a='ls -la' you should use a=$(ls -la), it doesn't preserve newlines however, I'm not sure how to save the output with newlines, using a pipe might be your best option.

[AncientPC]

1)

ting@Kin:~$ acpi -b
Battery 1: charging, 57%, 01:13:01 until charged

What's the best way to get 57% from the above line?

Edit: After reading the rest of your post I got the result by doing this:

ting@Kin:~$ acpi -b | cut -f2 -d"," | sed -e 's/[[:space:]]//g'
62%

Is there an easier way to trim leading and trailing white space?

Is there anyway to get the information through regexp pattern matching (i.e. an in-line grep) as opposed to removing what I don't want?

2) Thanks, I didn't know about head or cut, they make it much easier.

3)

ting@Kin:~$ echo abc123def | sed -e 's/[[:digit:]]//g'
abcdef
ting@Kin:~$ echo abc123def | sed -e '/[[:digit:]]/d'
ting@Kin:~$

4) Thanks, exactly what I was looking for.

[stylishpants]

1)

ting@Kin:~$ acpi -b
Battery 1: charging, 57%, 01:13:01 until charged

What's the best way to get 57% from the above line?

Edit: After reading the rest of your post I got the result by doing this:

ting@Kin:~$ acpi -b | cut -f2 -d"," | sed -e 's/[[:space:]]//g'
62%

Is there an easier way to trim leading and trailing white space?

Is there anyway to get the information through regexp pattern matching (i.e. an in-line grep) as opposed to removing what I don't want?


Sure, here are some ways:



# egrep uses POSIX regexps
# -o flag prints only the match, not the rest of the line
acpi -b | egrep -o '[0-9]+%'

# Perl uses perl-style regexps of course
# Remove the l flag if you don't want a newline automatically appended
# See these man pages for more info: perlre perlrun
acpi -b | perl -nle 'print $& if /\d+%/'



1)

2) Thanks, I didn't know about head or cut, they make it much easier.

3)

ting@Kin:~$ echo abc123def | sed -e 's/[[:digit:]]//g'
abcdef
ting@Kin:~$ echo abc123def | sed -e '/[[:digit:]]/d'
ting@Kin:~$

4) Thanks, exactly what I was looking for.

[Mr. C.]

3) What is it you don't understand? sed -e 's/<regex>//g' does the same as sed -e '/<regex>/d'.

Convince yourself that your two sed expressions do not produce the same results. Or let this convince you:


$ echo -e 'line one\nline two' | sed -e 's/one//g'
line
line two
$ echo -e 'line one\nline two' | sed -e '/one/d'
line two
$


4) Instead of a='ls -la' you should use a=$(ls -la), it doesn't preserve newlines however, I'm not sure how to save the output with newlines, using a pipe might be your best option.

The two forms of are equivalent. Output assigned to variables has newlines converted to spaces. This behavior can be changed if necessary, but it rarely is.

AncientPC - no need to use temporary files when assigning output to a variable is cheaper, more convenience (no cleanup) and less error prone.

MrC

[ghostdog74]

1)

ting@Kin:~$ acpi -b
Battery 1: charging, 57%, 01:13:01 until charged

What's the best way to get 57% from the above line?

the best way:
acpi -b |awk '{print $NF}'


Edit: After reading the rest of your post I got the result by doing this:

ting@Kin:~$ acpi -b | cut -f2 -d"," | sed -e 's/[[:space:]]//g'
62%

Is there an easier way to trim leading and trailing white space?

not necessary if using awk method

[AncientPC]

The two forms of are equivalent. Output assigned to variables has newlines converted to spaces. This behavior can be changed if necessary, but it rarely is.

How come echo 'ls -al' doesn't return what I want but echo $(ls -al) does?

Thanks to everyone who replied. This is what I've ended up with:

#/bin/bash
#format: #time,battery %,load

output=/var/log/battery.log

time=$(date +%H:%M,)
battery=$(acpi -b | gawk '{print $4}')
load=$(w | head -n1 | gawk '{print $NF}')

echo $time$battery$load >> $output

exit

[Mr. C.]

How come echo 'ls -al' doesn't return what I want but echo $(ls -al) does?

I thought they were backquotes -I see now they are single quotes. I was trying to clarify that backquotes anad $() command substitution were the same. Sorry for the noise.

MrC