fthedit - Edit one or more header keywords in the input HDU.
fthedit infile[ext] @editfile.txt
fthedit infile[ext] keyword operation value
fthedit edits the header keywords in the input FITS HDU in place,
modifying the original file. There are 2 main ways to use fthedit:
- Modify multiple keywords at once by specifying an ASCII template
file which lists the keywords to be added or deleted in the header.
- Modify, append, or delete a single keyword (or delete all instances
of the keyword) by specifying the
components of the keyword with the 'keyword', 'value', 'unit', and
'comment' parameters. In this mode, the keyword may also be inserted
at a specific location in the header, or a specified keyword can be
overwritten with a new keyword.
In the first mode of use, each line of the 'editfile' text file
contains a template for a keyword that is to be appended, modified
or deleted in the header:
- To modify an existing keyword or to append a
new keyword, add a line to the 'editfile' that contains the name,
value, and comment field of the keyword in free format, as in:
keyword = value / [units] comment
EXPOSURE = 3.5 / [s] total exposure time
OBJECT M31 name of observed object
COMMENT this is a general comment
HISTORY provides file processing history information
Note that the equal sign and slash character are optional. In most cases
the value of a string type keyword does not need to be enclosed in quotes,
unless the value could be confused with a numeric or boolean value.
- To delete a keyword, add a line to 'editfile' containing the name
of the keyword preceded by a minus sign, as in:
- To rename a keyword, add a line to 'editfile' containing
the current name of the keyword, preceded by a minus sign,
followed by the new name of the keyword, as in:
- Any lines in 'editfile' that begin with the pound sign '#' or consist
entirely of 7 or fewer space characters are ignored by fthedit and are
treated as comment lines. Lines beginning with 8 or more space
characters are interpreted as a FITS comment keyword with a blank name.
- If the keyword name is longer than 8 characters or contains special
characters that are not allowed in a true FITS keyword name, then the
FITS record will be constructed using the ESO HIERARCH convention. For
example, if the keyword template looks like:
CCD$camera:shutter_speed = 0.1 / [s] shutter speed
then the FITS header recorde will be written as:
HIERARCH CCD$camera:shutter_speed = 0.1 / [s] shutter speed
where the effective keyword 'name' is 'CCD$camera:shutter_speed'.
To run fthedit in the other "single keyword" mode of use, enter the type of
edit to be performed ('add', 'delete', 'replace', or 'deleteall')
in the 'operation' parameter.
- If operation = add, then the specified 'keyword' will be modified
if it already exists, or added to the header if not. The commentary
keywords such as COMMENT or HISTORY are always added to the header.
The keyword record is formed by concatenating the 'keyword', 'value',
'unit' and 'comment' parameter strings into one long string, then
reformatting it to conform to the rules for a FITS keyword. Note that the
'value', 'unit', and 'comment' parameters are somewhat redundant and
the unit and comment strings can be specified as part of the 'value'
parameter if desired. An error will be returned if an attempt is made
to modify a write-protected keyword (see the 'protect' parameter). If
the 'insert' parameter is not blank it will be interpreted as the name
or sequence number of an existing keyword in the header after which the
new keyword should be inserted.
- If operation = delete, then the specified 'keyword' name (or the
first instance of that keyword if there are more than one) will
be deleted from the input HDU.
- If operation = deleteall, then all instances of the specified
'keyword' name will be deleted from the input HDU. This is
useful for deleting all the HISTORY or COMMENT keywords in a header.
Wild card characters (*, ? or #) may also be used when specifying the keyword
name, where * matches any string of characters, ? matches any single
character, and # matches any consecutive string of decimal digits. Example:
?COEF# will match all keywords where the 2nd through 5th characters
are the string 'COEF' followed by one or more digits. All the keywords
that match the template will be deleted.
- If operation = replace, then the 'keyword' and 'value' parameters
take on slightly different meanings: 'keyword' is used to supply a
text search string. The first non-protected header keyword that
contains this case-sensitive string, anywhere in the 80-character
length of the header record, will be overwritten by the string given by
the 'value' parameter. In this case, 'value' gives the entire new
keyword string, including name, value, and comment string if relevant,
for the new keyword. The value string is not reformatted by fthedit
(only the first 8 characters will be capitalized if necessary) so the
string must conform to all the rules governing the format of a FITS
keyword. The 'replace' operation is especially useful for modifying
COMMENT or HISTORY keywords which cannot generally be modified with the
'add' operation because there are usually more than one keyword with
the same name.
- infile [filename]
- File name and optional extension name or number enclosed in square
brackets of the HDU to be modified (e.g., 'infile.fits' or
infile.fits[events]'). If a specific extension name or number is not
specified, then the first 'interesting' HDU (e.g., the first image HDU
that has more than 0 dimensions, or the first table HDU that is not a
Good Time Interval extension) will be opened and operated upon.
- keyword [string]
- This parameter has 2 modes of use.
1) It may give the name of an ASCII text file, preceded by the '@'
character, that contains a list of the edit operations to be performed.
Each line of this file specifies a keyword to be added, modified, or
deleted in the header.
2) If the string does not begin with the '@' character, then it is used
to specify the name of the keyword to be added or deleted (case
insensitive), or, if operation = replace, then a unique text search
string (case sensitive). In the latter case, the first non-protected
80-character header keyword that contains this string (in the keyword
and/or value and/or comment fields) will be replaced in its entirety by
the text string given by the 'value' parameter.
- operation [string]
- Type of edit operation to be performed if no 'editfile' is
specified. Valid operations are 'add' or 'a' to add or update a
keyword, 'delete' or 'd' to delete a keyword, 'deleteall' to delete
all instances of a keyword, and 'replace' or 'r' to
overwrite an existing keyword with a new keyword. This parameter is
ignored when the name of a text file is entered for the 'keyword'
- value [string]
- The value (and optional comment field) of the keyword to be added,
or, if operation = replace, the entire 80-character record that will
overwrite the header record identified by the 'keyword' parameter
search string. The datatype of the keyword value is determined by
context. String values can be enclosed in single quotes. Boolean
keywords may have a value of T or F. This parameter is ignored if
operation = delete or if the name of a text file is entered for the
- (unit = " ") [string]
- Optional physical units of the value (e.g., 'km/s'). This string
will be written enclosed in square brackets at the beginning of the
keyword comment field. This parameter is only used if operation = add.
- (comment = " ") [string]
- Optional comment string for the keyword. The comment string may be
entered as part of the value parameter instead. This parameter is only
used if operation = add.
- (insert = " ") [string]
- If operation = add, then this parameter gives the name or sequence
number of the keyword after which the new keyword will be inserted. If
'insert' is blank, then the new keyword will either be updated if it
already exists or appended to the end of the header if not.
- (protect = YES) [boolean]
- If protect = YES, then the mandatory keywords that define the
structure of the HDU will be write protected and may not be edited.
This includes the SIMPLE, BITPIX, NAXIS, NAXISn, PCOUNT, GCOUNT,
TFORMn, TBCOLn, keywords. Setting protect = NO will allow any of these
keywords to be modified or deleted, which if done improperly, can
corrupt the input file and make it completely unreadable! One should
always make a backup copy of the file before trying to edit the
- (longstring = NO) [boolean]
- If longstring = YES, then string keywords whose values are too
long (> 68 characters) to fit in a single FITS header keyword will be
written using the HEASARC Long String Keyword convention. The value
string is divided up into 68-character segments, and each segment
is written in sequence to multiple header keywords. All the subsequent
continued keywords will have "CONTINUE" in the first 8 characters of
the header record. Note that this option currently can only be used
in the "single keyword" mode, and it does not support
inserting the new keyword at a specific location in the header.
If the value string contains embedded space characters then the
whole string must be enclosed with single quote characters. If the
value string is given on the unix command line, then this quoted string
must in turn be enclosed with double quote characters (e.g.,
"'This is the long string value'").
- (chatter = 1) [integer, 0 - 5]
- Controls the amount of informative text written to standard
output. Setting chatter = 5 will produce detailed diagnostic output,
otherwise this task normally does not write any output.
- (history = NO) [boolean]
- If history = YES, then a set of HISTORY keywords will be written to
the header of the input file to record the current value of all the
fthedit task parameters.
Note that when commands are issued on the Unix command line, strings
containing special characters such as '[' or ']' must be enclosed in
single or double quotes.
1. This example illustrates the multi-keyword edit mode in which
the edit commands are contained in the 'editfile.txt' text file.
fthedit infile.fits @editfile.txt
Here is an example of an edit file. Note that the equal sign and
slash field delimiters are normally optional in the template file,
and the keyword names need not be given in upper case.
# the following lines insert or update keywords
object = 'Mira star' / name of observed object
ra = 146.5677 / [deg] Right Ascension
dec -45.4343 [deg] Declination
nobs 45 sequence number
COMMENT this comment is written verbatim
HISTORY file processed by Joe Bloggs on 04-03-2001
# the following lines delete existing keywords
# the following lines rename keywords
2. Append the EXPOSURE keyword or update the value and comment fields
if the EXPOSURE keyword already exists. The 2 examples shown here produce
exactly the same result.
fthedit infile.fits keyword=exposure operation=add
value=11000.0 unit=s comment='nominal exposure time'
fthedit infile.fits none add exposure
value='11000.0 / [s] nominal exposure time'
Both of these commands will create the following header keyword:
EXPOSURE= 11000.0 / [s] nominal exposure time
3. Insert a new TDISP2 keyword immediately following the TFORM2 keyword.
fthedit infile.fits TDISP2 add F8.2
comment='column display format' insert=TFORM2
will insert the following header keyword:
TDISP2 = 'F8.2 ' / column display format
4. Insert a new COMMENT keyword following the 10th keyword currently in
fthedit infile.fits COMMENT add
'All times are given in units of seconds.' insert=10
will insert the following header keyword:
COMMENT All times are given in units of seconds.
5. Change the value of the SIMPLE keyword in the primary array. Since
this keyword is normally write protected, the 'protect' parameter must
be set to NO.
fthedit 'infile.fits' SIMPLE add F
comment='non-conforming FITS file' protect=NO
will modify the following header keyword:
SIMPLE = F / non-conforming FITS file
6. Delete the EQUINOX keyword.
fthedit infile.fits EQUINOX delete
7. Modify a COMMENT keyword containing the string "preliminary data".
fthedit infile.fits keyword='preliminary data' replace
value='COMMENT This file contains final processed data.'
The original keyword looked like this:
COMMENT This file contains preliminary data.
After running fthedit, the keyword now looks like this:
COMMENT This file contains final processed data.
8. Delete a particular HISTORY keyword in the header that contains the
string "horizontal axis". Since there are often multiple HISTORY
keywords in the header it is usually not possible to delete one
directly. Instead the 'replace' operation is used to rename the
HISTORY keyword to a unique keyword ('DUMMY' in this example) then
fthedit is run a second time to delete the DUMMY keyword.
fthedit infile.fits keyword='horizontal axis' replace
value='DUMMY = 0'
fthedit infile.fits DUMMY delete
fv, the interactive FITS file editor, can also be used to edit FITS header keywords.
The design of this task is based on the fmodhead, fkeypar, and fmodcomm
tasks in the ftools package and the CXC dmhedit task.