shell tricks

hex_to_decimal.sh

h2d () {
  for hex in $*; do
    HEX=$(echo "$hex" | tr [:lower:] [:upper:])
    echo "ibase=16;$HEX" | bc
  done;
}

d2h () {
  for DEC in $*; do
    echo "obase=16;$DEC" | bc
  done;
}

monitor.sh

# Watch traffic coming back from a server on localhost:3000 
tcpdump -s 4096 -Ani lo0 src port 3000

# list processes with PGID
ps j

# signal all processes in current PGID
kill [SIG] 0

tricks.sh

# check to see if a url returns 200 in the response header, ex 'HTTP/1.1 200 OK'
curl -sI URL | head -n 1 | grep -q ' 200 '

# perform a sed operation and only print the results of matching lines
# note that on OSX sed does not like multiple commands separated by
# semicolons - so separate them with -e for portability or use a long
# form.
sed -e 's/abc/xyz/' -e 't p' -e 'd' -e ':p' << DOC
abc
abcdef
defabc
def
DOC

# or just...
sed -ne 's/abc/xyz/p' << DOC
abc
abcdef
defabc
def
DOC

sed -e 's/abc/xyz/
t p
d
:p
' <<DOC
abc
abcdef
defabc
def
DOC

# Paste tables together like a bad-ass
cat > one.txt <<DOC
abc
pqr
xyz
DOC
cat > two.txt <<DOC
123
456
789
DOC
paste one.txt two.txt 
# abc	123
# pqr	456
# xyz	789
cat one.txt two.txt | paste - - -
# abc	pqr	xyz
# 123	456	789

# sed character classes
echo 'documents/421450709.xml' | sed -e 's/[[:digit:]]\{1,\}/ID/'

# curl with IPv6 (http://tech.bluesmoon.info/2011/12/using-curl-with-ipv6-addresses.html)
curl "http://\[2600:xxx:yyy::zzz\]/page.html"

# remove whitespace lines, in place, for all files in pwd
# 
#   sed -e 's/ \{1,\}$//' -i '' *
#
# but do something like this for goodness sake!
find lib -type f | grep -v -E '^.git' | xargs sed -e 's/ \{1,\}$//' -i ''

# prefix lines matching a pattern
sed -e 's/.*b.*/. &/' -e 't z' -e 's/./x &/' -e ':z' <<DOC
abc
bcd
cde
DOC

# partition a file by regexp
sed -e '/b/ {
  w one
  d
}' > two <<DOC
abc
bcd
cde
DOC

# print a stream of entries by a pattern
# * branch to show for new entries
# * append the line to the hold buffer if not a new entry
# * branch to the end of the file unless the last line (ie show on the last line)
#
# then in show x to start a new entry in the hold buffer and retrieve the entry
# currently in it. then print the entry if it matches some pattern
sed -ne '
  /==/ b show
  H
  $ !b
  :show
  x
  /d/p
' << DOC
==
abc
==
bcd
==
cde
DOC

# man pages in mate
# modified from: http://jasonrudolph.com/blog/2008/03/14/manning-up-textmate-meets-man-pages/
man ab | col -bx | mate

# multiple heredocs
cat <<DOC | while read line; do echo $line; cat <<DOX; done
abc
xyz
DOC
123
456
DOX