UNIX> cat f1 And she's buying UNIX> cat f2 a stairway to heah ven UNIX> cat f1 f2 And she's buying a stairway to heah ven UNIX> cat f1 f2 > f3 UNIX> cat f3 And she's buying a stairway to heah ven UNIX>Remember, when using either the Bourne shell or csh, you cannot redirect standard output to be a file that you're using as input. Why? Because both shells create the output file before running the command. Thus, you'll lose the input file before the command gets executed.
NOTE:
Most of you running csh have a variable 'noclobber' set. This makes it
"safe" to use the same file as input and output. It tells csh not to
destroy an existing file, instead give a warning and terminate the command.
BUT, this "safety" may lull you into a false sense of security because it
does NOT affect the operation of any scripts you may use. I would like you
to either run the Bourne shell in a window to test the examples or do the
following in a window
UNIX> unset noclobberwhich will make csh act like sh.
UNIX> cat f3 And she's buying a stairway to heah ven UNIX> cat f3 > f3 cat: input/output files 'f3' identical UNIX> cat f3 UNIX> cat f1 f2 > f3 UNIX> cat f3 And she's buying a stairway to heah ven UNIX> cat < f3 > f3 cat: input/output files '-' identical UNIX> cat f3 UNIX>
UNIX> cat sth And when we wind on down the road Our shadow's taller than our souls There walks a lady we all know Who shines bright lights and wants to know Why all that glitters is not gold These lyrics are all old as mold UNIX> cat -ve sth And when we wind on down the road$ Our shadow's taller than our souls$ There walks a lady we all know$ Who shines subliminal message^H^H^H^H^H^H^H^H^H^H^H^H^H^H^H^H^H^Hbright lights and wants to know $ Why all that glitters is not gold$ These lyrics are all old as mold$ UNIX>Second, -n prepends the line number to each line. E.g.
UNIX> cat md See Saw, Margery Daw Johnny will have a new Master He will get but a penny a day Because this poem is a disaster! UNIX> cat -n md 1 See Saw, Margery Daw 2 Johnny will have a new Master 3 He will get but a penny a day 4 Because this poem is a disaster! UNIX>Third, if you intermix - with the filenames, cat will use standard input when it reaches the -:
UNIX> echo "This is a tiresome song" | cat f1 - f2 And she's buying This is a tiresome song a stairway to heah ven UNIX>Irritatingly, even cat has different implementations on different machines. Thus, -e works in one way on one machine, and another on another. For example, try -e on SunOS and Solaris machines. Or -s. This is very frustrating if you are trying to write portable shell scripts. My philosophy on this is to not use options which are not portable. This means that before you write a shell script that you are going to send to someone you should test it out on many machines and operating systems. A good way to break a shell script that runs on a BSD machine (like SunOS or Ultrix) is to try it on a System V machine (like Solaris or HPUX). It is frustrating, but you must do it.
UNIX> cat md See Saw, Margery Daw Johnny will have a new Master He will get but a penny a day Because this poem is a disaster! UNIX> sort md Because this poem is a disaster! Johnny will have a new Master He will get but a penny a day See Saw, Margery Daw UNIX>Use -r to sort in reverse order, and -n to sort numerically rather than lexicographically:
UNIX> cat gstats 9 8 8.99 6.99 Steve Elkington 14 10 12.28 7.19 Brad "Chicken Neck" Faxon 1 1 10.87 10.87 Tom Kalinowski 12 10 10.13 7.16 Tom Lehman 7 6 9.46 6.87 Greg Norman 14 11 10.02 5.94 Jesper Parnevik 9 9 5.10 5.10 Nick Price 10 10 5.63 5.63 Tiger Woods UNIX> sort gstats 1 1 10.87 10.87 Tom Kalinowski 10 10 5.63 5.63 Tiger Woods 12 10 10.13 7.16 Tom Lehman 14 10 12.28 7.19 Brad "Chicken Neck" Faxon 14 11 10.02 5.94 Jesper Parnevik 7 6 9.46 6.87 Greg Norman 9 8 8.99 6.99 Steve Elkington 9 9 5.10 5.10 Nick Price UNIX> sort -n gstats 1 1 10.87 10.87 Tom Kalinowski 7 6 9.46 6.87 Greg Norman 9 8 8.99 6.99 Steve Elkington 9 9 5.10 5.10 Nick Price 10 10 5.63 5.63 Tiger Woods 12 10 10.13 7.16 Tom Lehman 14 10 12.28 7.19 Brad "Chicken Neck" Faxon 14 11 10.02 5.94 Jesper Parnevik UNIX> sort -r gstats 9 9 5.10 5.10 Nick Price 9 8 8.99 6.99 Steve Elkington 7 6 9.46 6.87 Greg Norman 14 11 10.02 5.94 Jesper Parnevik 14 10 12.28 7.19 Brad "Chicken Neck" Faxon 12 10 10.13 7.16 Tom Lehman 10 10 5.63 5.63 Tiger Woods 1 1 10.87 10.87 Tom Kalinowski UNIX> sort -nr gstats 14 11 10.02 5.94 Jesper Parnevik 14 10 12.28 7.19 Brad "Chicken Neck" Faxon 12 10 10.13 7.16 Tom Lehman 10 10 5.63 5.63 Tiger Woods 9 9 5.10 5.10 Nick Price 9 8 8.99 6.99 Steve Elkington 7 6 9.46 6.87 Greg Norman 1 1 10.87 10.87 Tom Kalinowski UNIX>(2) Sort lets you break up the input into "fields", and sort on a particular field. The default delimiter for fields is white space. You specify the sorting field with -k n, where n is the number of the field. You can also specify a range of fields with -k n,m .To sort, the first field is 1. ` If you want to sort (numerically) using the third column of gstats, you do:
UNIX> sort -n -k 3 gstats 9 9 5.10 5.10 Nick Price 10 10 5.63 5.63 Tiger Woods 9 8 8.99 6.99 Steve Elkington 7 6 9.46 6.87 Greg Norman 14 11 10.02 5.94 Jesper Parnevik 12 10 10.13 7.16 Tom Lehman 1 1 10.87 10.87 Tom Kalinowski 14 10 12.28 7.19 Brad "Chicken Neck" Faxon UNIX>And if you want to sort by the golfers' first names, you do:
UNIX> sort -k 5 gstats 14 10 12.28 7.19 Brad "Chicken Neck" Faxon 7 6 9.46 6.87 Greg Norman 14 11 10.02 5.94 Jesper Parnevik 9 9 5.10 5.10 Nick Price 9 8 8.99 6.99 Steve Elkington 10 10 5.63 5.63 Tiger Woods 1 1 10.87 10.87 Tom Kalinowski 12 10 10.13 7.16 Tom Lehman UNIX>When sorting lexicographically, sort includes white space, which seems odd. To have it ignore leading white space in a field, you use the -b option. Thus, to sort a file lexicographically, and ignore leading white space, you do:
UNIX> sort -b -k 1 md Because this poem is a disaster! He will get but a penny a day Johnny will have a new Master See Saw, Margery Daw UNIX>NOTE:
The last two important options of sort are -u, which strips out duplicates, and -f which ignores the distinction between upper and lower case. As always, read the man page for more info and more options.
Please note the changes in Debian. Though the lecture note for Unix system will not be changed. Checking out the man page in the current operating system is always a good idea. Please also note the usage of echo. The equivalent utility to mailx is nail in Debian.
The examples I used in class are:
>echo 'cat md' | at +1minute >echo 'cat md' | at +2minute >echo 'cat md' | at 2pm >atq 14 2005-09-26 12:45 a ytang 15 2005-09-26 12:46 a ytang 16 2005-09-26 14:00 a ytang >atrm 16 >atq 15 2005-09-26 12:46 a ytangJob 14 is not displayed anymore because it is already executed. If you don't use echo, you will probably receive error messages. Try it out. Here is the original UNIX class note: ******************************
at [ -c | -k | -s ] [-f file] [-m] timespecBy default at uses the SHELL variable to determine which shell to use to execute the commands. You can change this with the -s which says to treat the script as a Bourne shell script. The other two options are for ksh or csh respectively. If you don't specify a file, then it uses standard input.
When the proper time comes about, the operating system (specifically, the cron daemon) will execute a process under your ownership that first cd's to the directory in which you made the at call, and then runs the script. If there is output to the job, the at will email you the output. A note here. If the directory is only mounted while YOU are logged in to that particular machine (like your home area) then you cannot log out and expect at to be able to work. Use cron instead.
At is a great program. The main problem with it is that there is no real standard at syntax. Some versions don't support the -s command line argument. Some let you specify relative times (like "at now + 1 hour"). Some don't. However, most of the time, it doesn't matter. If you give at a time without a date, it assumes that you mean the nearest date with that time.
For example, suppose it is 4:00 PM, on June 17, 1997. The following at commands will send mail to your boss at 2:00 AM on June 18:
UNIX> cat bossmail Hi Boss, See how late I'm working? I think I deserve a raise!!! Me UNIX> at 2am at> mailx -s 'an idea' your_boss_email < bossmail at>To see what jobs you have currently queued up, do atq or at -l:warning: commands will be executed using /bin/csh job 866613600.a at Wed Jun 18 02:00:00 1997 UNIX> at 2am June 18 at> mailx -s 'an idea' your_boss_email < bossmail at> warning: commands will be executed using /bin/csh job 866613601.a at Wed Jun 18 02:00:00 1997 UNIX> echo "mailx -s 'an idea your_boss_email < bossmail" | at 2am June 18 warning: commands will be executed using /bin/csh job 866613602.a at Wed Jun 18 02:00:00 1997 UNIX>
UNIX> atq Rank Execution Date Owner Job Queue Job Name 1st Jun 18, 1997 02:00 jplank 866613600.a a stdin 2nd Jun 18, 1997 02:00 jplank 866613601.a a stdin 3rd Jun 18, 1997 02:00 jplank 866613602.a a stdin UNIX> at -l 866613600.a Wed Jun 18 02:00:00 1997 866613601.a Wed Jun 18 02:00:01 1997 866613602.a Wed Jun 18 02:00:02 1997 UNIX>And if you have a change of heart and want to remove the jobs, use at -r or atrm. Note that all systems don't support all of these -- sometimes you have to hunt around to figure out how at and related commands work. As always, read the man page.
UNIX> at -r 866613600.a UNIX> at -l 866613601.a Wed Jun 18 02:00:01 1997 866613602.a Wed Jun 18 02:00:02 1997 UNIX> atrm 866613601.a 866613602.a 866613601.a: removed 866613602.a: removed UNIX> at -lIf at -s does not work on your system and you want to run a Bourne shell script, do
UNIX> echo 'sh scriptname' | at time
UNIX> grep pattern [ files ]If you don't specify files on the command line, then it will use standard input. It prints out all lines in the specified files that contain the pattern. If you specified more than one file on the command line, then it will prepend the line with the file that it came from. Examples:
UNIX> grep penny md He will get but a penny a day UNIX> grep penny < md He will get but a penny a day UNIX> grep all md sth sth:Our shadow's taller than our souls sth:There walks a lady we all know sth:Why all that glitters is not gold sth:These lyrics are all old as mold UNIX>The pattern is a ``regular expression.'' While they're not exactly the same as regular expressions in something like CS380, they're pretty close. I'll borrow from the grep and ed man pages to define regular expressions:
UNIX> cat greptest Jim Plank This string contains no numbers This string does though (1) -9.00 G0 V0LS UNIX> grep '[Gg]' greptest This string contains no numbers This string does though (1) G0 V0LS UNIX> grep '[0-9]' greptest This string does though (1) -9.00 G0 V0LS UNIX> grep '[A-Z]' greptest Jim Plank This string contains no numbers This string does though (1) G0 V0LS UNIX> grep '[^A-Za-z ]' greptest This string does though (1) -9.00 G0 V0LS UNIX>
UNIX> grep '^.........$' greptest Jim Plank UNIX>To grep for lines with at least 9 characters, do:
UNIX> grep '.........' greptest Jim Plank This string contains no numbers This string does though (1) UNIX>To grep for lines that end with two numbers, do:
UNIX> grep '[0-9][0-9]$' greptest -9.00 UNIX>
UNIX> grep all sth Our shadow's taller than our souls There walks a lady we all know Why all that glitters is not gold These lyrics are all old as mold UNIX> grep '\<.ll\>' sth There walks a lady we all know Why all that glitters is not gold These lyrics are all old as mold UNIX> grep 'dow\>' sth Our shadow's taller than our souls UNIX> grep '\<.\>' sth Our shadow's taller than our souls (matching the s in "shadow's") There walks a lady we all know UNIX>
UNIX> grep 'Z*' md See Saw, Margery Daw Johnny will have a new Master He will get but a penny a day Because this poem is a disaster! UNIX>Here are some more examples. The first greps for two words separated by a space (actually, since * can match zero, this will also match a single space, or a word before or following a single space). The second greps for a period followed by any number of zeros, and then the end of line. The last greps for any line with two zeros somewhere.
UNIX> grep '^[^ ]* [^ ]*$' greptest Jim Plank G0 V0LS UNIX> grep '\.0*$' greptest -9.00 UNIX> grep '0.*0' greptest -9.00 G0 V0LS UNIX>
UNIX> grep '0\{1\}' greptest
-9.00
G0 V0LS
This is equivalent to grepping for 000*:
UNIX> grep '0\{2,\}' greptest
-9.00
Here we grep for 5-letter words containing just lower case letters,
then 5-letter words, then words of at least 5 letters:
UNIX> grep '\<[a-z]\{5\}\>' greptest
UNIX> grep '\<[A-Za-z]\{5\}\>' greptest
Jim Plank
UNIX> grep '\<[A-Za-z]\{5,\}\>' greptest
Jim Plank
This string contains no numbers
This string does though (1)
UNIX>
If you want to make sure that grep prints out the file name
of the file that the line comes from, include /dev/null on
the command line. Then you'll have at least two files on the command
line, and grep will be sure to print the file name:
UNIX> grep '\<.ld\>' sth These lyrics are all old as mold UNIX> grep '\<.ld\>' sth /dev/null sth:These lyrics are all old as mold UNIX>grep can do far more than this -- you need to read the man page to figure it all out. Also you should read about egrep and fgrep. The newest manpage for /usr/bin/grep does not really tell you WHICH regular expressions it uses. Assume 'basic' regular expressions and read the man pages for regex(5) and regexp(5). And you may still get it wrong but its better than the alternative.
First, to find a file with a specific name in all directories reachable from x (this one), do:
find x -name name -printFor examples, to find all .c files reachable from your home directory, do:
UNIX> find $HOME -name '*.c' -print /mahogany/homes/plank/src/jgraph/work/draw.c /mahogany/homes/plank/src/jgraph/work/edit.c /mahogany/homes/plank/src/jgraph/work/exit.c /mahogany/homes/plank/src/jgraph/work/jgraph.c /mahogany/homes/plank/src/jgraph/work/libmalloc.c /mahogany/homes/plank/src/jgraph/work/list.c /mahogany/homes/plank/src/jgraph/work/printline.c /mahogany/homes/plank/src/jgraph/work/prio_list.c /mahogany/homes/plank/src/jgraph/work/process.c /mahogany/homes/plank/src/jgraph/work/show.c ... UNIX>Note that you should put the '*' in single quotes. Also, note that find will not traverse '..', nor will it normally traverse soft links to other directories. Sometimes this is a drag, but it's pretty much for the best. Suppose you wanted to find all the core files reachable from the current directory. Then you do:
UNIX> find . -name core -printNote the way that you match files is using the shell's wildcarding, and not using regular expressions. In other words, if you want to find all your files with two-letter names, do:
UNIX> find $HOME -name '??' -printIf you want to print all files reachable from your home directory, do
UNIX> find $HOME -printUsing find to find filenames is something I do so much that I have a shell script called jf that finds all files reachable from the current directory that contain a given string:
UNIX> jf md find . -name '*md*' -print ./md UNIX> jf g find . -name '*g*' -print ./greptest ./gstats UNIX>The second use of find is to grep through all files to find a certain string. For example, suppose I want to find if the word "no" exists in any files reachable from . (current directory). Then I'd do:
UNIX> find . -type f -exec grep no {} \;
This string contains no numbers
1 1 10.87 10.87 Tom Kalinowski
There walks a lady we all know
Who shines bright lights and wants to know
Why all that glitters is not gold
UNIX>
Great, so it exists. Here's how you find out what file it's in:
UNIX> find . -type f -exec grep no {} /dev/null \;
./greptest:This string contains no numbers
./gstats:1 1 10.87 10.87 Tom Kalinowski
./sth:There walks a lady we all know
./sth:Who shines bright lights and wants to know
./sth:Why all that glitters is not gold
UNIX>
You'll find that you end up doing things like this more than you'd
imagine, especially if you're kind of forgetful, like I am.
Lastly, suppose that you want to remove all of your core files. Then you do (I put the -i in so that you'll be prompted -- leave it off if you don't want to be prompted):
UNIX> find $HOME -name core -exec rm -i {} \;
rm: remove /mahogany/homes/plank/src/ohhell/core? y
rm: remove /mahogany/homes/plank/src/jgammon/core? y
...
etc
There's a lot going on here, but this is the simple way to do it. You should
read the man page for find to figure out exactly what's going on.
Some people find find to be quite confusing, especially the
-exec part, where you have to put a backslash before the semi-colon.
Give it a read. You will also see that on the Solaris systems that find has
an option that lets it traverse soft links. I have tried this and it was really
ugly. If you ever try to do this, make SURE you know what is going on first.
And it is not portable.