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shell [2014/02/27 11:31]
dblume [expect tips]
— (current)
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-====== shell tips ====== 
- 
-===== Quick Tips ===== 
- 
-The [[http://www.reddit.com/r/bashtricks/comments/hdfzc/execute_previous_command_as_root/|History Expansion character]] is "!".  To search the history for a previous "scp" command and only print it, try the first line below. But if you want to interactively find that command, type ''<Ctrl>+r,scp''. 
- 
-<code bash> 
-$ !?scp?:p 
-$ ^rscp 
-</code> 
- 
-===== bash expansion ===== 
- 
-<code bash> 
-$ cp file{,.bk} 
-</code> 
- 
-expands to 
- 
-<code bash> 
-$ cp file file.bk 
-</code> 
- 
-Replace all files that end with .JPG to .jpeg 
- 
-<code bash> 
-for file in *.JPG; do mv $file ${file%.JPG}.jpeg; done 
-for file in *.JPG; do mv $file ${file/JPG/jpeg}; done 
-</code> 
- 
-Then there are two different "rename" commands: 
- 
-<code bash> 
-rename .JPG .jpg *.JPG  
-rename "s/JPG/jpg/" *.JPG  
-</code> 
- 
- 
-===== Command Template ===== 
- 
-Here's a template for shell commands that demonstrates a number of arguments, length of argument, etc.  It could still stand a bit of clean-up according to the [[http://google-styleguide.googlecode.com/svn/trunk/shell.xml|Google Shell Style Guide]]. 
- 
-<code bash> 
-#!/bin/bash 
-set -euf -o pipefail # See: https://sipb.mit.edu/doc/safe-shell/ 
- 
-declare -r SCRIPT_NAME=$(basename "$BASH_SOURCE") 
- 
-## exit the shell (default status code: 1) after printing the message to stderr 
-die() { 
-    echo >&2 "$1" 
-    exit ${2-1} 
-} 
- 
-## the options used by this script 
-DISK=e 
-declare -i VERBOSE=0 
- 
-## exit the shell (with status 2) after printing the message 
-usage() { 
-    echo "\ 
-$SCRIPT_NAME -hv [Drive Letter] (default: $DISK) 
-    -h      Print this help text 
-    -v      Enable verbose output 
-" 
-    exit 2; 
-} 
- 
-## Process the options 
-while getopts "hv" OPTION 
-do 
-  case $OPTION in 
-    h) usage;; 
-    v) VERBOSE=1;; 
-    \?) usage;; 
-  esac 
-done 
- 
-## Process the arguments 
-shift $(($OPTIND - 1)) 
- 
-if [ $# -eq 0 ]; then 
-    : # Let the default be used 
-elif [ $# -eq 1 ]; then 
-    if [ ${#1} -eq 1 ]; then 
-        DISK=$1 
-    else 
-        # 64 is EX_USAGE from sysexits.h 
-        die "$SCRIPT_NAME: Drive Letter can only be one character long." 64 
-    fi 
-else 
-    usage; 
-fi 
- 
-## Lock this if only one instance can run at a time 
-# UNIQUE_BASE=${TMPDIR:-/tmp}/"$SCRIPT_NAME".$$ 
-LOCK_FILE=${TMPDIR:-/tmp}/"$SCRIPT_NAME"_"$DISK".lock 
-if [ -f "$LOCK_FILE" ]; then 
-  die "$SCRIPT_NAME is already running. ($LOCK_FILE was found.)" 
-fi 
-trap "rm -f $LOCK_FILE" EXIT 
-touch $LOCK_FILE 
- 
-## The main work of this script 
- 
-if [ ! -d /cygdrive/"$DISK"/backup/Users ]; then 
-    mkdir -p /cygdrive/"$DISK"/backup/Users 
-fi 
- 
-((VERBOSE==1)) && echo "Starting at `date`" 
-rsync /cygdrive/c/Users/me /cygdrive/"$DISK"/backup/Users 
-</code> 
- 
-===== Miscellaneous Shell Tips ===== 
- 
-If you want a single column of just the file and path names, you can get it like so: 
- 
-<code bash> 
-ls --format=single-column 
-</code> 
- 
-But if you don't know what you're doing, you might construct something like so: 
- 
-<code bash> 
-ls -Al | tr -s ' ' | cut -d ' ' -f10- 
-</code> 
- 
-  - List "almost all" items in "long" format (one line per item) 
-  - Squeeze repeats of the space character 
-  - Cut out everything from before the 10th column and show everything afterwards. 
- 
-Of course, if you could assert the following: 
- 
-  * none of the first columns were repeats (awk would only identify the first repeated column) 
-  * the desired column didn't have delimiters in it (filenames with spaces) 
- 
-...you could use awk 
- 
-<code bash> 
-... | awk '{print $10}' 
-</code> 
- 
-Anyway, given a list of directories, they can be inserted into a cp command with xargs if you need. 
- 
-<code bash> 
-cat list_of_directories_at_one_level.txt | xargs -I {} cp -r $SOURCEDIRPREFIX:{} $DEST 
-</code> 
- 
-Useful bash command for finding strings within python files... 
- 
-<code bash> 
-find . -name \*.py -type f -print0 | xargs -0 grep -nI "timeit" 
-</code> 
- 
-Interesting way to use ''grep -v'' to remove paths from a list generated by ''find''.  Not sure about the escaped ''|'' character, though... 
- 
-<code bash> 
-#!/bin/bash 
-find $PWD -regex ".*\.[hcHC]\(pp\|xx\)?" | \ 
-    grep -v " \|unwantedpath/unwantedpath2\|unwantedpath3" > cscope.files 
-cscope -q -b 
-</code> 
- 
-Here's how to find if a symbol is in a library, and how to search lots of object files and print the filename above the search... 
- 
-<code bash> 
-nm obj-directory/libmyobject.a | c++filt | grep Initialize_my_obj 
-find bindirectory/ -name \*.a -exec nm /dev/null {} \; 2>/dev/null | \ 
-    c++filt | grep -P "(^bindirectory.*\.a|T Initialize_my_obj)" 
-</code> 
- 
-Also handy to merge two streams together... 
- 
-<code bash> 
-( cat file1 && cat file2 ) | sort 
-</code> 
- 
-When a little quick math is needed, use ''bc'' 
-<code bash> 
-$ bc <<< "obase=16;ibase=10;15" 
-F 
-$ bc -l <<< 1/3 
-.33333333333333333333 
-$ bc <<< "scale=2; 1/3" 
-.33 
-$ bc <<< "obase=10;ibase=16;B" 
-11 
-</code> 
- 
-and, when coverting from hex to dec... 
- 
-<code bash> 
-echo $((0x2dec)) 
-</code> 
- 
-But, then again, does that really seem easier than, 
- 
-<code> 
-python -c "print int('B',16)" 
-</code> 
- 
-There's a bash way to calculate how many days ago a date was: 
- 
-<code bash> 
-$ echo $(( ($(date +%s) - $(date -d "2012-4-16" +%s)) / 86400 )) 
-</code> 
- 
-And a Python way... 
- 
-<code python> 
-python -c "import datetime; print (datetime.date.today() - datetime.date( 2012, 4, 16 )).days" 
-</code> 
- 
-And for displaying lines clipped at the right edge of the window instead wrapped: 
- 
-<code bash> 
-cat_one_line_per_row() { 
-  cat "$@" | expand | cut -b1-$COLUMNS 
-} 
-</code> 
- 
-or a "clip" command like so: 
- 
-<code bash> 
-alias clip="expand | cut -b1-\$COLUMNS" 
-</code> 
- 
-ctags's man page says that one of its bugs is that it has too many options.  Ain't that the truth.  Make note of the obscure flag here, ''--c++-kinds=+p'', that tells ctags to process prototypes and method declarations. 
- 
-<code bash> 
-ctags -n --if0=yes --c++-kinds=+p --langmap=c++:+.inl.lst \ 
-    --langmap=asm:+.inc --file-tags=yes -R --extra=fq \ 
-    --exclude=unwanted_file.lst \ 
-    --exclude='*unwanted-directory*/*' \ 
-    --regex-C++='/^.*CINIT.(.+),.*,.*,.*/CURLOPT_\1/' 
-</code> 
- 
-When you want to repeat a command a few times... 
-<code bash> 
-seq 1 50 | xargs -I{} -n1 echo '{} Hello World!' 
-</code> 
- 
-Keywords: bash shell sh zsh 
- 
-====== .vimrc tips ====== 
- 
-Here's an alternative way to automatically save backups (with dates in the filename) everytime you save a file. 
-<code> 
-set backup 
-set backupdir=~/.vim/backup/ 
-au BufWritePre * let &bex = '-' . strftime( "%Y%m%d-%H%M%S" ) 
-</code> 
- 
-That makes a lot of files, so you can clean out the backups with a cron job like this: 
- 
-<code> 
-# at 3 in the morning on Mondays, delete files older than 30 days 
-0 3 * * 1 find $HOME/.vim/backup/ -type f -mtime +30 -delete 
-</code> 
- 
-====== expect tips ====== 
- 
-What to do when it's not sure you're going to make a connection? 
- 
-<code> 
-set times 0 
-set made_connection 0 
-set timeout 120 
-while { $times < 2 && $made_connection == 0 } { 
-    spawn nc $SERVER 
-    send "\r" 
-    expect { 
-        "login:" { 
-            send "john.doe\r" 
-            set made_connection 1 
-        } eof { 
-            sleep 1s 
-            set times [ expr $times + 1 ] 
-        } timeout { 
-            puts "Didn't expect to timeout." 
-            exit 
-        } 
-    } 
-} 
-</code> 
- 
-I think the following is wrong-headed. It's not usually the case that spawn will fail. 
- 
-<code> 
-set times 0; 
-while { $times < 2 && $made_connection == 0 } { 
-    if { [ catch { spawn nc $SERVER } pid ] } { 
-        set times [ expr $times + 1 ]; 
-        sleep 1s; 
-    } else { 
-        set made_connection 1 
-    } 
-} 
-</code> 
- 
-====== Perl tips ====== 
- 
-The module ''Search::Dict'' has a "''loop''" function that can be used to do a binary search in an ordered dictionary file (a logfile (or log file) that starts with timestamps works). ''File::SortedSeek'' might also be recommended. 
- 
  
shell.1393529499.txt.gz · Last modified: 2014/02/27 11:31 by dblume
 
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