Coby Viner gave a technical talk at a lab meeting about GNU Parallel, a tool for executing jobs in parallel using one or more computers. Viner covered why GNU Parallel is useful, basic examples from its tutorial on syntax and usage, additional syntax for more complex tasks, and real examples of how they have used it. The talk provided an overview and introduction to GNU Parallel for parallelizing tasks, with a focus on explaining its syntax and capabilities through examples.

1. LAB MEETING—
TECHNICAL
TALK
COBY VINER
USE CASES
BASIC EXAMPLES
BASIC SYNTAX
ADDITIONAL
SYNTAX
MORE EXAMPLES
REAL EXAMPLES
LAB MEETING—TECHNICAL TALK
GNU PARALLEL
O. TANGE, “GNU PARALLEL - THE COMMAND-LINE
POWER TOOL”, ;login: The USENIX Magazine, VOL. 36, NO.
1, PP. 42–47, FEB. 2011
Coby Viner
Hoffman Lab
Wednesday, April 13, 2016

2. LAB MEETING—
TECHNICAL
TALK
COBY VINER
USE CASES
BASIC EXAMPLES
BASIC SYNTAX
ADDITIONAL
SYNTAX
MORE EXAMPLES
REAL EXAMPLES
OVERVIEW
WHY USE GNU PARALLEL?
BASIC EXAMPLES FROM THE TUTORIAL
BASIC ELEMENTS OF SYNTAX [FROM THE TUTORIAL]
MUCH MORE SYNTAX FOR MANY OTHER TASKS
MORE TUTORIAL EXAMPLES
SOME EXAMPLES OF MY GNU PARALLEL USAGE

3. LAB MEETING—
TECHNICAL
TALK
COBY VINER
USE CASES
BASIC EXAMPLES
BASIC SYNTAX
ADDITIONAL
SYNTAX
MORE EXAMPLES
REAL EXAMPLES
WHY USE GNU PARALLEL?
a shell tool for executing jobs in parallel using one
or more computers.

4. LAB MEETING—
TECHNICAL
TALK
COBY VINER
USE CASES
BASIC EXAMPLES
BASIC SYNTAX
ADDITIONAL
SYNTAX
MORE EXAMPLES
REAL EXAMPLES
WHY USE GNU PARALLEL?
a shell tool for executing jobs in parallel using one
or more computers.
Easily parallelize perfectly parallel tasks

5. LAB MEETING—
TECHNICAL
TALK
COBY VINER
USE CASES
BASIC EXAMPLES
BASIC SYNTAX
ADDITIONAL
SYNTAX
MORE EXAMPLES
REAL EXAMPLES
WHY USE GNU PARALLEL?
a shell tool for executing jobs in parallel using one
or more computers.
Easily parallelize perfectly parallel tasks
For each chromosome. . .

6. LAB MEETING—
TECHNICAL
TALK
COBY VINER
USE CASES
BASIC EXAMPLES
BASIC SYNTAX
ADDITIONAL
SYNTAX
MORE EXAMPLES
REAL EXAMPLES
WHY USE GNU PARALLEL?
a shell tool for executing jobs in parallel using one
or more computers.
Easily parallelize perfectly parallel tasks
For each chromosome. . .
For each sex, for each technical replicate, for each
hyper-parameter(s)

7. LAB MEETING—
TECHNICAL
TALK
COBY VINER
USE CASES
BASIC EXAMPLES
BASIC SYNTAX
ADDITIONAL
SYNTAX
MORE EXAMPLES
REAL EXAMPLES
WHY USE GNU PARALLEL?
a shell tool for executing jobs in parallel using one
or more computers.
Easily parallelize perfectly parallel tasks
For each chromosome. . .
For each sex, for each technical replicate, for each
hyper-parameter(s)
Job submission scripts within a for loop

8. LAB MEETING—
TECHNICAL
TALK
COBY VINER
USE CASES
BASIC EXAMPLES
BASIC SYNTAX
ADDITIONAL
SYNTAX
MORE EXAMPLES
REAL EXAMPLES
WHY USE GNU PARALLEL?
a shell tool for executing jobs in parallel using one
or more computers.
Easily parallelize perfectly parallel tasks
For each chromosome. . .
For each sex, for each technical replicate, for each
hyper-parameter(s)
Job submission scripts within a for loop
Improved, cleaner, syntax (for the programmer), even in
serial

9. LAB MEETING—
TECHNICAL
TALK
COBY VINER
USE CASES
BASIC EXAMPLES
BASIC SYNTAX
ADDITIONAL
SYNTAX
MORE EXAMPLES
REAL EXAMPLES
WHY USE GNU PARALLEL?
a shell tool for executing jobs in parallel using one
or more computers.
Easily parallelize perfectly parallel tasks
For each chromosome. . .
For each sex, for each technical replicate, for each
hyper-parameter(s)
Job submission scripts within a for loop
Improved, cleaner, syntax (for the programmer), even in
serial
Facile interleaving of tasks, in the order one is thinking
about them

10. A BASIC [MAN PAGE] EXAMPLE: “WORKING
AS XARGS -N1. ARGUMENT APPENDING”
find . -name '*.html' | parallel gzip --best

11. A BASIC [MAN PAGE] EXAMPLE: “WORKING
AS XARGS -N1. ARGUMENT APPENDING”
find . -name '*.html' | parallel gzip --best
find . -type f -print0 |
parallel -q0 perl -i -pe 's/FOO BAR/FUBAR/g'

12. LAB MEETING—
TECHNICAL
TALK
COBY VINER
USE CASES
BASIC EXAMPLES
BASIC SYNTAX
ADDITIONAL
SYNTAX
MORE EXAMPLES
REAL EXAMPLES
EASY INSTALLATION FROM SOURCE

13. LAB MEETING—
TECHNICAL
TALK
COBY VINER
USE CASES
BASIC EXAMPLES
BASIC SYNTAX
ADDITIONAL
SYNTAX
MORE EXAMPLES
REAL EXAMPLES
EASY INSTALLATION FROM SOURCE

14. LAB MEETING—
TECHNICAL
TALK
COBY VINER
USE CASES
BASIC EXAMPLES
BASIC SYNTAX
ADDITIONAL
SYNTAX
MORE EXAMPLES
REAL EXAMPLES
EASY INSTALLATION FROM SOURCE

15. LAB MEETING—
TECHNICAL
TALK
COBY VINER
USE CASES
BASIC EXAMPLES
BASIC SYNTAX
ADDITIONAL
SYNTAX
MORE EXAMPLES
REAL EXAMPLES
EASY INSTALLATION FROM SOURCE

16. LAB MEETING—
TECHNICAL
TALK
COBY VINER
USE CASES
BASIC EXAMPLES
BASIC SYNTAX
ADDITIONAL
SYNTAX
MORE EXAMPLES
REAL EXAMPLES
EASY INSTALLATION FROM SOURCE

17. ANOTHER BASIC [MAN PAGE] EXAMPLE:
“INSERTING MULTIPLE ARGUMENTS”
bash: /bin/mv: Argument list too long
ls | grep -E '.log$' | parallel mv {} destdir

18. ANOTHER BASIC [MAN PAGE] EXAMPLE:
“INSERTING MULTIPLE ARGUMENTS”
bash: /bin/mv: Argument list too long
ls | grep -E '.log$' | parallel mv {} destdir
ls | grep -E '.log$' | parallel -m mv {} destdir

19. BASIC ELEMENTS OF SYNTAX [FROM THE
TUTORIAL]
Input:
parallel echo ::: A B C # command line
cat abc-file | parallel echo # from STDIN
parallel -a abc-file echo # from a file

20. BASIC ELEMENTS OF SYNTAX [FROM THE
TUTORIAL]
Input:
parallel echo ::: A B C # command line
cat abc-file | parallel echo # from STDIN
parallel -a abc-file echo # from a file
Output [line order may vary]:
A
B
C

21. BASIC ELEMENTS OF SYNTAX [FROM THE
TUTORIAL]
Multiple inputs.
Input:
parallel echo ::: A B C ::: D E F
cat abc-file | parallel -a - -a def-file echo
parallel -a abc-file -a def-file echo
cat abc-file | parallel echo :::: - def-file # alt. file
parallel echo ::: A B C :::: def-file # mix cmd. and file

22. BASIC ELEMENTS OF SYNTAX [FROM THE
TUTORIAL]
Multiple inputs.
Input:
parallel echo ::: A B C ::: D E F
cat abc-file | parallel -a - -a def-file echo
parallel -a abc-file -a def-file echo
cat abc-file | parallel echo :::: - def-file # alt. file
parallel echo ::: A B C :::: def-file # mix cmd. and file
Output [line order may vary]:
A D
A E
A F
B D
B E
B F
C D
C E
C F

23. BASIC ELEMENTS OF SYNTAX [FROM THE
TUTORIAL]
Matching input.
Input:
parallel --xapply echo ::: A B C ::: D E F

24. BASIC ELEMENTS OF SYNTAX [FROM THE
TUTORIAL]
Matching input.
Input:
parallel --xapply echo ::: A B C ::: D E F
Output [line order may vary]:
A D
B E
C F

25. BASIC ELEMENTS OF SYNTAX [FROM THE
TUTORIAL]
Matching input.
Input:
parallel --xapply echo ::: A B C ::: D E F
Output [line order may vary]:
A D
B E
C F
-xapply will wrap, if insufficient input is provided.

26. BASIC ELEMENTS OF SYNTAX [FROM THE
TUTORIAL]
Replacement strings: The 7 predefined replacement strings
Input:
parallel echo {} ::: A/B.C
parallel echo {.} ::: A/B.C
Output:
A/B.C
A/B

27. BASIC ELEMENTS OF SYNTAX [FROM THE
TUTORIAL]
Replacement strings: The 7 predefined replacement strings
Input:
parallel echo {} ::: A/B.C
parallel echo {.} ::: A/B.C
Output:
A/B.C
A/B
Rep. String Result
. remove ext.
/ remove path
// only path
/. only ext. and path
# job number
% job slot number

28. BASIC ELEMENTS OF SYNTAX [FROM THE
TUTORIAL]
Customizing replacement strings
-extensionreplace to change {.} etc.
Shorthand custom (PCRE+) replacement strings
GNU parallel’s 7 replacement strings:
--rpl '{} '
--rpl '{#} $_=$job->seq()'
--rpl '{%} $_=$job->slot()'
--rpl '{/} s:.*/::'
--rpl '{//} $Global::use{"File::Basename"}
||= eval "use File::Basename; 1;"; $_ = dirname($_);'
--rpl '{/.} s:.*/::; s:.[^/.]+$::;'
--rpl '{.} s:.[^/.]+$::'

29. BASIC ELEMENTS OF SYNTAX [FROM THE
TUTORIAL]
Multiple input sources and positional replacement:
parallel echo {1} and {2} ::: A B ::: C D

30. BASIC ELEMENTS OF SYNTAX [FROM THE
TUTORIAL]
Multiple input sources and positional replacement:
parallel echo {1} and {2} ::: A B ::: C D
Always try to define replacements, with {<>} syntax.

31. BASIC ELEMENTS OF SYNTAX [FROM THE
TUTORIAL]
Multiple input sources and positional replacement:
parallel echo {1} and {2} ::: A B ::: C D
Always try to define replacements, with {<>} syntax.
Test with --dry-run first.

32. MUCH MORE SYNTAX FOR MANY OTHER TASKS
--pipe: instead of STDIN as command args, data sent to
STDIN of command

33. MUCH MORE SYNTAX FOR MANY OTHER TASKS
--pipe: instead of STDIN as command args, data sent to
STDIN of command
command_A | command_B | command_C, where
command_B is slow

34. MUCH MORE SYNTAX FOR MANY OTHER TASKS
--pipe: instead of STDIN as command args, data sent to
STDIN of command
command_A | command_B | command_C, where
command_B is slow
Remote execution to directly parallelize over multiple
machines

35. MUCH MORE SYNTAX FOR MANY OTHER TASKS
--pipe: instead of STDIN as command args, data sent to
STDIN of command
command_A | command_B | command_C, where
command_B is slow
Remote execution to directly parallelize over multiple
machines
Working directly with a SQL database

36. MUCH MORE SYNTAX FOR MANY OTHER TASKS
--pipe: instead of STDIN as command args, data sent to
STDIN of command
command_A | command_B | command_C, where
command_B is slow
Remote execution to directly parallelize over multiple
machines
Working directly with a SQL database
Shebang: often cat input_file | parallel command,
but can do #!/usr/bin/parallel --shebang -r echo

37. MUCH MORE SYNTAX FOR MANY OTHER TASKS
--pipe: instead of STDIN as command args, data sent to
STDIN of command
command_A | command_B | command_C, where
command_B is slow
Remote execution to directly parallelize over multiple
machines
Working directly with a SQL database
Shebang: often cat input_file | parallel command,
but can do #!/usr/bin/parallel --shebang -r echo
As a counting semaphore: parallel --semaphore or sem

38. MUCH MORE SYNTAX FOR MANY OTHER TASKS
--pipe: instead of STDIN as command args, data sent to
STDIN of command
command_A | command_B | command_C, where
command_B is slow
Remote execution to directly parallelize over multiple
machines
Working directly with a SQL database
Shebang: often cat input_file | parallel command,
but can do #!/usr/bin/parallel --shebang -r echo
As a counting semaphore: parallel --semaphore or sem
Default is one slot: a mutex

39. ANOTHER [MAN PAGE] EXAMPLE:
“AGGREGATING CONTENT OF FILES”
parallel --header : echo x{X}y{Y}z{Z} >
x{X}y{Y}z{Z}
::: X {1..5} ::: Y {01..10} ::: Z {1..5}

40. ANOTHER [MAN PAGE] EXAMPLE:
“AGGREGATING CONTENT OF FILES”
parallel --header : echo x{X}y{Y}z{Z} >
x{X}y{Y}z{Z}
::: X {1..5} ::: Y {01..10} ::: Z {1..5}
parallel eval 'cat {=s/y01/y*/=} >
{=s/y01//=}' ::: *y01*
This runs: cat x1y*z1 > x1z1, ∀x∀z

41. POST-MEME2IMAGES INKSCAPE
CONVERSIONS FOR PUBLICATION-READY
CENTRIMO PLOTS AND SEQUENCE LOGOS
parallel inkscape --vacuum-defs --export-pdf={.}.pdf {}
::: "$centrimo_eps_1" "$centrimo_eps_2"

42. POST-MEME2IMAGES INKSCAPE
CONVERSIONS FOR PUBLICATION-READY
CENTRIMO PLOTS AND SEQUENCE LOGOS
parallel inkscape --vacuum-defs --export-pdf={.}.pdf {}
::: "$centrimo_eps_1" "$centrimo_eps_2"
parallel "inkscape --vacuum-defs --export-pdf={.}.pdf {};
pdfcrop --hires --clip --margins '0 0 0 -12' {.}.pdf;
mv -f {.}-crop.pdf {.}.pdf
" ::: logo+([:digit:])$VECTOR_FILE_EXT

43. FIXING DIRECTORY STRUCTURES—SYMBOLIC
LINK ISSUES (FOR DATA PROVENANCE)
parallel --dry-run -j 1 --rpl
'{s} s@.*?((?:fe)?male_d+-d+).*@$1@' "{s};
ln -s /$(readlink {}) {}"
::: $(find . -mindepth 3 -maxdepth 3 -xtype l)

44. FIXING DIRECTORY STRUCTURES—SYMBOLIC
LINK ISSUES (FOR DATA PROVENANCE)
parallel --dry-run -j 1 --rpl
'{s} s@.*?((?:fe)?male_d+-d+).*@$1@' "{s};
ln -s /$(readlink {}) {}"
::: $(find . -mindepth 3 -maxdepth 3 -xtype l)
parallel --rpl
'{s} s:.+?/(.+?)_peaks.narrowPeak.gz$:
1_summits.bed.gz:'
"ln -s ../../linked-2015-10-07-.../data/MACS/{s}
{//}/" ::: */*_peaks.narrowPeak.gz

45. FIXING DIRECTORY STRUCTURES—SYMBOLIC
LINK ISSUES (FOR DATA PROVENANCE)
parallel --dry-run -j 1 --rpl
'{s} s@.*?((?:fe)?male_d+-d+).*@$1@' "{s};
ln -s /$(readlink {}) {}"
::: $(find . -mindepth 3 -maxdepth 3 -xtype l)
parallel --rpl
'{s} s:.+?/(.+?)_peaks.narrowPeak.gz$:
1_summits.bed.gz:'
"ln -s ../../linked-2015-10-07-.../data/MACS/{s}
{//}/" ::: */*_peaks.narrowPeak.gz
parallel -j 1 --rpl '{...} s:/.*::;'
"dir=$(readlink -f {} |
sed -r 's:/linked.+?/:/{...}/:');
mkdir $dir; rm -f {}; ln -s $dir {//}/M-ChIP_runs"
::: $(find linked-2016-01-31-* -type l -name 'M-ChIP_runs')

46. EXPLORING/COLLATING COMPLEX CENTRIMO
RESULTS
parallel --dry-run -j 1
--rpl '{sex} s:.*?(w*male)-d+_d+.*:1:'
--rpl '{rep} s:.*?male-(d+_d+).*:1:'
--rpl "{TFinfo} s:.*?([^/]+)-expandedTo500bpRegions-
mod.*:1:"
--rpl '{thresh} s:.*?d+_d+-(0.d+).*:1:'
"awk '$0 !~ /^#/ {$1=""; $2="";
print "{TFinfo}","{sex}","{rep}","
{thresh}"$0;}' {} |
sed -r 's/[[:space:]]+/t/g'"
::: $(find ../MEME-ChIP_runs-initial_controls/
-mindepth 5 -wholename
'*hypothesis_testing_selected_controlledVars/
centrimo_out/centrimo.txt' | head
)

47. PROCESSING CHIP-SEQ PEAK DATA WITH
MACS
parallel --rpl '{/..SRF} s:../w+[-.](SRFw*).*:$1:i;'
macs14 callpeak -t {} -n {/..SRF} -g 'mm'
-s 51 --bw 150 -S -p 0.0001
::: ../*.alignment.mm8.bed.gz

48. PROCESSING CHIP-SEQ PEAK DATA WITH
MACS
parallel --rpl '{/..SRF} s:../w+[-.](SRFw*).*:$1:i;'
macs14 callpeak -t {} -n {/..SRF} -g 'mm'
-s 51 --bw 150 -S -p 0.0001
::: ../*.alignment.mm8.bed.gz
parallel "zcat {} | awk 'BEGIN{FS=OFS="t"} NR > 1
{print $2,$3,$4;}' |
pigz -9 > {/.}.bed.gz" ::: ../*MACS_peaks_annot.txt.gz
liftoverAll '.bed.gz'

49. PROCESSING CHIP-SEQ PEAK DATA WITH
MACS
function liftoverAll {
parallel liftOver {} "$LIFTOVER_CHAIN_FILE_FULL_PATH"
../$LIFTED_OVER_DIR_NAME/{/.}.liftedmm9
../$LIFTED_OVER_DIR_NAME/{/.}.unlifted
::: *"$1"
pigz -9 ../$LIFTED_OVER_DIR_NAME/*.liftedmm9
../$LIFTED_OVER_DIR_NAME/*.unlifted
}

50. PROCESSING CHIP-SEQ PEAK DATA WITH
MACS
function liftoverAll {
parallel liftOver {} "$LIFTOVER_CHAIN_FILE_FULL_PATH"
../$LIFTED_OVER_DIR_NAME/{/.}.liftedmm9
../$LIFTED_OVER_DIR_NAME/{/.}.unlifted
::: *"$1"
pigz -9 ../$LIFTED_OVER_DIR_NAME/*.liftedmm9
../$LIFTED_OVER_DIR_NAME/*.unlifted
}
parallel -j ${NSLOTS:=1} --xapply
--rpl '{r} s:.*RS(d+).*:1:'
"$MACS_CMD_AND_COMMON_PARAMS -f BAMPE -n 'M-r{1r}'
-t {1} -c {2} |& tee -a '$OUT_DIR/M-r{1r}.log'"
::: $IN_DIR/1494*@(1|2|3).bam
::: $IN_DIR/1494*@(4|5|6).bam

51. PIPELINE—PROCESSING BISULFITE
SEQUENCING DATA WITH METHPIPE
merge_methcount_cmds=$(
parallel -j $NSLOTS --joblog "x.log"
--rpl '{-../} s:.*/::; s:(.[^.]+)+$::; s:-d+$::;'
--dry-run
"echo "$MODULE_LOAD_CMD export LC_ALL=C;
cat $ALIGNED_DIR/{-../}*.tomr |
sort -k 1,1 -k 2,2n -k 3,3n -k 6,6 | ldots |
methcounts -v -c $BISMARK_REF
-o $COUNTS_DIR/{-../}_pool_ALL.meth /dev/stdin"
| tee -a /dev/stderr | qsub ldots
::: $IN_DIR/*.1.fastq.gz | sort -V | uniq
)