One of our printing applications runs an external program which does some magic and sometimes returns a barcode in EPS format to be printed on the document.
if [ ... some magic ]
then
gnu-barcode -b $1 -c -e code39 -u mm -t 1x3 > $TMP.ps
ps2epsi $TMP.ps $TMP.eps
cat $TMP.eps
rm -f $TMP.eps $TMP.ps
else
cat /dev/null
fi
This works OK. However, it generates an annoying warning on the printing application side about not receiving a valid EPS when the else ... runs and we do cat /dev/null. I need to return a blank but valid EPS instead of the cat /dev/null. How can I accomplish this?
The EPS format is defined in Adobe Technical note 5002, its available on the web but it moves around so much I won't attempt to post a URL. However, unless you are a PostScript programmer that probably won't help you.
The simplest possible valid EPS would be something like:
%!PS-Adobe-2.0 EPSF-3.0
%%BoundingBox:0 0 0 0
That's the only required content in an EPSF. Of course, a real printing application might not like a BoundingBox of 0 0 0 0.
Related
I'm using instruments inside a bash script on a continuous integration server.
I would like to know when a command as failed in the script, so I can exit prematurely from it and mark the build as failed.
instruments displays a LOG ERROR to the console, but I don't succeed in getting a return value.
How can I achieve this?
if have:
instruments -w "iPhone 6 (8.3 Simulator)" -t
it is possible to do something like:
if(...)
then ...
Thanks in advance
Fairly easy:
instruments -w "iPhone 6 (8.3 Simulator)" -t
if (( $? > 0 ))
then
echo "instruments commands failed with error: $?" >&2
fi
The (( )) notation is for an arithmetic comparison. String pattern comparisons are done using [[ ... ]]. Be careful to use the correct spacing, in general whitespace is used as a separator in shells, so it can be significant.
An alternative syntax could be:
if instruments -w "iPhone 6 (8.3 Simulator)" -t
then
echo "it worked"
else
echo "it failed"
fi
and that is often preferable. But I think in this case the style I show fits better with what you need.
The special variable ? gives the return value of the previous command. Prefixing with a $ gives us the variable's value. By convention, a return value of zero means success, 1-255 means an error (the range on UNIX/Linux is 0-255, one byte). The significance of each error number is application specific, so you must read the documentation to find what it means.
Remember that $? gives us the return value of the previous command, so even an echo would reset it!
The >&2 means "send the output to the standard error stream". Error messages should go here, which is also known s stderr, file descriptor 2. It is a nice thing to do if you are redirecting output from the script.
EDIT: After all that, Apple does not appear to document an exit code for the instruments command, I checked the man page. That's poor in my opinion, but there's not much you can do. In languages like C (and probably ObjC) if the program ends without setting an exit code you just get any old value that is lying about in memory. So you cannot even rely on zero being success - unless you know otherwise?
I have literally been at this for 5 hours, I have busybox on my device, and I unfortunately do not have -X in grep to make my life easier.
edit;
I have two list both of them have mac addresses, essentially I am just wanting to achieve offline mac address lookup so I don't have to keep looking it up online
list.txt has vendor mac prefix of course this isn't the complete list but just for an example
00:13:46
00:15:E9
00:17:9A
00:19:5B
00:1B:11
00:1C:F0
scan will have list of different mac addresses unknown to which vendor they go to. Which will be full length mac addresses. when ever there is a match I want the line in scan to be output.
Pretty much it does that, but it outputs everything from the scan file, and then it will output matching one at the end, and causing duplicate. I tried sort -u, but it has no effect its as if there is two different output from two different methods, the reason why I say that is because it will instantly output scan file that has everything in it, and couple seconds later it will output the matching one.
From searching I came across this
#!/bin/bash
while read line; do
grep -F 'list' 'scan'
done < list.txt
which displays the duplicate result when/if found, the output is pretty much echoing my scan file then displaying the matched pattern, this creating duplicate
This is frustrating me that I have not found a solution after click on all the links in google up to page 9.
Please someone help me.
I don't know if the Busybox sed supports this out of the box, but it should be easy to do in Awk or Perl instead then.
Create a sed script to print lines from file2 which are covered by a prefix in file1 by transforming each line in file1 into a sed command to print a match for that regular expression:
sed 's%.*%/&/p%' file1 | sed -n -f - file2
The same in Awk:
awk 'NR==FNR { a[++i]="^" $0; next }
{ for (j=1; j<=i; ++j) if ($0 ~ a[j]) print }' file1 file2
Ok guys I did a nested for loop (probably very in efficient) but I got it working printing the matching mac addresses using this
#!/usr/bin/bash
for scanlist in `cat scan | cut -d: -f1,2,3`
do
for listt in `cat list`
do
if [[ $scanlist == $listt ]]; then
grep $scanlist scan
fi
done
done
if anyone can make this more elegant but it works for me for now. I think the problem I had was one list contained just 00:11:22 while my other list contained 00:11:22:33:44:55 that is why I cut it on my scanlist to make same length as my other list. So this only output the matches instead of doing duplicate output.
I am writing a csh script that will extract a line from a file xyz.
the xyz file contains a no. of lines of code and the line in which I am interested appears after 2-3 lines of the file.
I tried the following code
set product1 = `grep -e '<product_version_info.*/>' xyz`
I want it to be in a way so that as the script find out that line it should save that line in some variable as a string & terminate reading the file immediately ie. it should not read furthermore aftr extracting the line.
Please help !!
grep has an -m or --max-count flag that tells it to stop after a specified number of matches. Hopefully your version of grep supports it.
set product1 = `grep -m 1 -e '<product_version_info.*/>' xyz`
From the man page linked above:
-m NUM, --max-count=NUM
Stop reading a file after NUM matching lines. If the input is
standard input from a regular file, and NUM matching lines are
output, grep ensures that the standard input is positioned to
just after the last matching line before exiting, regardless of
the presence of trailing context lines. This enables a calling
process to resume a search. When grep stops after NUM matching
lines, it outputs any trailing context lines. When the -c or
--count option is also used, grep does not output a count
greater than NUM. When the -v or --invert-match option is also
used, grep stops after outputting NUM non-matching lines.
As an alternative, you can always the command below to just check the first few lines (since it always occurs in the first 2-3 lines):
set product1 = `head -3 xyz | grep -e '<product_version_info.*/>'`
I think you're asking to return the first matching line in the file. If so, one solution is to pipe the grep result to head
set product1 = `grep -e '<product_version_info.*/>' xyz | head -1`
I'm trying to run this command to do some cleanups.
egrep -v -f ref_file.css my_file.css
However, it is giving me an error.
egrep: Unmatched ( or \ (
How can I go around that? I'm on mac terminal.
Thanks,
Tee
I know I'm a bit late, but maybe this can help other users looking for the same...
If you just want to check the differences between two files, then you can use diff, as mentioned in the comments. However, if the files are somewhat similar, and you are looking for a way to check the differences visually, then you can use sdiff file1 file2 to get a diff-ish output but showing the files side by side.
In the output, | between the two files means that the line is somewhat shared between the two files, but with differences in the text or format.
< and > means that the line to the left or to the right exists in the left or the right file, and not in the other, as you may have expected.
You may then grep the output from sdiff for ' | ', ' < ', and ' > ', and analize that in case you need to do further processing on the files...
With a "normal" (i mean "full") linux distro, it works just fine:
sleep $(echo "$[ ($RANDOM % 9 ) ]")
ok, it waits for about 0-9 sec
but under OpenWRT [not using bash, rather "ash"]:
$ sleep $(echo "$[ ($RANDOM % 9 ) ]") sleep: invalid number '$[' $
and why:
$ echo "$[ ($RANDOM % 9 ) ]" $[ ( % 9 ) ] $
So does anyone has a way to generate random numbers under OpenWRT, so i can put it in the "sleep"?
Thank you
You might try something like this:
sleep `head /dev/urandom | tr -dc "0123456789" | head -c1`
Which works on my WhiteRussian OpenWRT router.
I actually don't know if this will always return a number, but when it does, it will always return 0-9, and only 1 digit (you could make it go up to 99 if you made the second head -c2).
Good luck!
you could also use awk
sleep $(awk 'BEGIN{srand();print int(rand()*9)}')
For some scenarios, this might not yield a sufficient diversity of answers. Another approach is to use /dev/urandom directly (eg https://www.2uo.de/myths-about-urandom/):
echo $(hexdump -n 4 -e '"%u"' </dev/urandom)
When using awk, note that awk uses the time of day as the seed (https://linux.die.net/man/1/awk). This might be relevant for scenarios where the time of day is reset (eg no battery backed time of day clock), or synchronised across a fleet (eg group restart).
srand([expr])
Uses expr as a new seed for the random number generator. If no expr is provided, the time of day is used. The return value is the previous seed for the random number generator.
This is confirmed by looking at the source in busybox (https://github.com/mirror/busybox/blob/master/editors/awk.c):
seed = op1 ? (unsigned)L_d : (unsigned)time(NULL);
At least for some versions of Openwrt, it seems an explicit call to srand() is required to avoid obtaining the same answers repeatedly:
# awk 'BEGIN{print rand(), rand()}'
0 0.345001
# awk 'BEGIN{print rand(), rand()}'
0 0.345001