EVL

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Head

(since EVL 1.1)

Command prints to output first <num> records of input. Without option -n prints first 10 records.

Head

is to be used in EVS job structure definition file. <f_in> and <f_out> are either input and output file or flow name.

evl head

is intended for standalone usage, i.e. to be invoked from command line.

EVD is EVL data definition file, for details see evl-evd(5).

Synopsis

syntax/Head
Head
  <f_in> <f_out> [<evd>|-d <inline_evd>] [-n [-]<num>] [-s|--skip-parse]
  [--validate] [--skip-bom]
  [ -x|--text-input | --text-input-dos-eol | --text-input-mac-eol ]
  [ -y|--text-output | --text-output-dos-eol | --text-output-mac-eol ]

evl head
  [<evd>|-d <inline_evd>] [-n [-]<num>] [-s|--skip-parse]
  [--validate] [--skip-bom]
  [ -x|--text-input | --text-input-dos-eol | --text-input-mac-eol ]
  [ -y|--text-output | --text-output-dos-eol | --text-output-mac-eol ]
  [-v|--verbose]

evl head
  ( --help | --usage | --version )

Options

-d, --data-definition=<inline_evd>

either this option or the file <evd> must be presented. Example: -d ’id int, user_id string(6) enc=iso-8859-1’

-n, --records=[-]<num>

output first <num> records instead of the default first 10; or use -n -<num> to output all records except last last <num>

-s, --skip-parse

this option has no effect with ’–records <num>’ (i.e. the case first <num> records are read and the rest is ignored). But with ’–records -<NUM>’ it does not parse all fields, but ’jump’ over record separator, i.e. the separator of the last field. Be careful with this option, it is particularly good for ’csv’ files, when you want to skip some weird formatted footer for example, but might be a wrong solution when some fields are separated by the same character as the last one.

--skip-bom

skip utf-8 BOM (Byte order mark) from the beginning of input, i.e. EF BB BF. Windows usually add it to files in UTF8 encoding

--validate

without this option, no fields are checked against data types. With this option, all output fields are checked

-x, --text-input

suppose the input as text, not binary

--text-input-dos-eol

suppose the input as text with CRLF as end of line

--text-input-mac-eol

suppose the input as text with CR as end of line

-y, --text-output

write the output as text, not binary

--text-output-dos-eol

produce the output as text with CRLF as end of line

--text-output-mac-eol

produce the output as text with CR as end of line

Standard options:

--help

print this help and exit

--usage

print short usage information and exit

-v, --verbose

print to stderr info/debug messages of the component

--version

print version and exit

Examples

  1. print to stdout only first 10 records:
    evl head example.evd -xy <in.txt
    
  2. read the binary input and omit last 3 records without parsing them (i.e. they no need to have the data structure defined by evd):
    cat input.bin | evl head -sy -n-3 \
                      -d'id int sep=",", updated date sep="\n"' \
                        > output.txt